Let's analyze what Hedin said to Mia:
"What a pathetic display, even with you here, Mia."
"… Stop babbling. I have a small gap in my strength."
"Then fill it immediately. If you’re going to sit back and sleep peacefully, we’ll all be crushed."
Mia accepts that she has a small gap in her strength, which implies that she has lost a bit of physical condition, but what is really interesting are Hedin's demands and expectations of her.
Asking her to "fill her gap immediately" means that she has not weakened and can return to full physical form during that fight; I repeat, this is not real life, we are talking about a fantasy world. I don't see it as that complicated to understand, the falna numerically indicates the magnitude of physical abilities, do the statistics deteriorate by not using or practicing them? ... no. The value of the statistics is maintained, which means that no matter how many years pass, the adventurer will retain the strength, endurance, agility and dexterity that are engraved on his back, that is, the body does not weaken due to retirement.
You could argue that the combat skills have deteriorated because they are not engraved on the falna, but Hedin trusts that Mia will recover her fullness immediately and tells her that if she does not, everyone will be crushed, that is, he is placing his faith in her to win, an expectation that would be ridiculous if retirement had really weakened her irremediably.
In conclusion, considering that the status and therefore the body do not deteriorate with time and Hedin's confidence in her immediate recovery, it is clear that retirement does not weaken the adventurers. Conclusion consistent with what Ottar said, where he only talked about Mia's stagnation (she's still the same as she was when she left the family), and he didn't tell her at any point: "you're weaker than you were when you were active" or anything like that.
This whole retirement weakness thing comes from you trying to justify Anya's absence in the ranking due to her retirement weakness, implying that if she had the condition she had in Folkvangr she would appear in the ranking because as a member of Freya she would be better than any other level 4.
But as you see, that's an assumption based on trying to apply a real-life condition to the world of Danmachi, in which the evidence indicates that if you retire you stagnate but you don't weaken. Argument that I used to prove that not every member of Freya is superior to their counterparts from other families, given that Anya wouldn't occupy the first place in the ranking in any case. However, if you already accept that it is not a universal rule, we can conclude this argument.
As a final note on this, we have no way to compare Anya with her Folkvangr version but her current version is very powerful, has had magnificent results and has received multiple praises from the author, so saying that she was weakened by retirement, not only lacks sources to corroborate it but is a mere assumption based on real-world logic that does not apply in Danmachi.
However, it is an interesting topic to analyze where the 3 waitresses would be in the ranking; by 2020 there would not be much problem in them being below Raul, but now, do not think that I do not share your reservations about it.
The first thing is that Anya is not necessarily better than Lunor and Chloe for not falling to the Bringar, the novel is clear in explaining that she had an advantage in knowing their fighting methods, that was a key factor that the other 2 did not have. According to this reasoning, Lunor and Chloe would be better because they defeated Grer and Dvalinn while Anya did not show the ability to do so.
Could Raul fight as well against Ryuu as Lunor did or could he defeat any of the Gulliver brothers in single combat with a level boost? Honestly, he does not give that impression, although he has some things in his favor such as being an expert in martial arts as he demonstrated against Valleta, or that he has shown himself to be almost at the level of Anakitty, being surpassed by her only in the battle of Knossos, since he had a rescue role, which did not allow him to obtain much excelia. If we had seen more fights we could get an idea of what each one is capable of, hence why I insist that this series urgently needs more antagonists.
Also, you are being unfair by asking Raul to defeat Valleta to demonstrate his ability. How would he defeat a level 5 in single combat? But Anya has not achieved something similar either, or who are you referring to? Which higher level opponent did Anya defeat?
I've been able to notice that you only question Raul's position on them, should I interpret that as you have no qualms about accepting that they would go after Anakitty? A clear indication that I see that Aisha is stronger than them is that she was the one who was sent against Alfrigg, the strongest of the brothers, it is a common trope to send the most powerful against the most powerful.
Regarding Van, you deliberately omit that Bell was not in good shape, remember that Hogni said that his combat abilities were very basic, that he only showed genius when he had to repel deadly attacks, but could Van defeat the Bell that recovered and injured Hedin? Also, defeating someone in a duel does not necessarily prove that you are better, like in chess, sometimes the world champion loses a game against another grandmaster, but that victory does not rank him on the top of the world podium; to determine who is better, a match is played to 12 games generally where the one with the best score is proven as the best of the 2.
Omori said that Ais was stronger than Tiona, Tione and Bete but that in some duels she can lose against them, but Ais is still the best. Van could defeat Bell occasionally but couldn't Anakitty do the same? We have no way of knowing; However, the speed with which you level up is a clear indication of talent, look at all the powerful characters, all of them are characterized by having leveled up quickly, like Ais, Allen and Ryuu who went up to level 2 in a year. It's not conclusive proof but at least it's a clear indicator of talent that favors Anakitty over Van.
There would be much more clarity regarding these issues if Omori decided to end the fights, apart from the fact that there are almost no antagonists he also doesn't allow the duels to develop, how I hate this habit of his!!
From what I remember of the duel between Ais and Phryne, the latter was surprised by not being able to defeat Ais despite having much more status than her, which doesn't speak well of her, since Ais without her wind can only count on her lower base status. As for Bete, I don't mention beastization explicitly because it's his skill, everyone fights using their skills, so I don't see the need to point it out. As for it leveling him up to 7, I'd really love that to happen, but Omori isn't usually very precise when indicating the magnitude of the boosts, so it's premature to just assume that.
Compare Phryne and Allen's performance against Bete, you see a clear contrasting difference, and it's not due to the status since this difference wouldn't be much, so you can see that Phryne isn't a big deal, so it's not an incommensurable merit that Tsubaki is stronger than her. It seems more enlightening to me that Bete, Tiona and Tione will fight in the same adventure as her, leveling up and she won't, which denotes inferiority on her part despite being much older than them.
That's where you clearly see how the difference in professional approach has a clear effect on skill and development, perhaps if Tsubaki were a full-time adventurer she would be at the same level than them, but she isn't, she's a blacksmith.
As for Ottar, the second Hildis Vini, the one that Hedin deflected, he threw it with the intention of they overcome it, but if they couldn't and died, he thought it was because that was as far as they could go, so the question remains as to whether Ottar really held back in all stages of combat.
Ais doesn't specialize in duels, but in monsters, and losing her composure denotes inexperience on her part, but it's not her who has to prove that she's better than any other level 6 from another family, so it's not a big deal that she doesn't appear unfazed by a shock. In fact, the Gullivers were already nervous since they were separated, feeling fear of having to fight alone exacerbates the question of whether these level 5s would actually beat anyone else, in fact, with Grer's defeat at the hands of Lunor we already know for a fact that it's not like that.
Man, I find Alfrigg's thing very forced, the trope of strengthening through heroic resistance is common in shonen, but his power was 3 or 4 times what he had moments before, so, unless he has a very broken skill, it was a plot convenience so that the girls wouldn't attack Allen and he could continue his dialogue with Anya and Hogni and then display his magic.