I honestly don't think what you said could be considered as mistakes. It seems more like you are talking about elements of the story in the series you think the series would be better without.

The only things I would consider "mistakes" would be;

1. elements of the story that contradicts of parts of the story, whether if that was in setting or timeline

or 2. spelling mistakes or grammer.

The only mistake I ever noticed Oomori make for 1 was that he described Tiona and Tione in volumes 1-4 as level 3 supporters and then when he wrote SO1 onward they were level 5 and not supporters instead other members of Loki's familia that were previously never mentioned like Lefiya were now the supporters. I don't really think that it is a big deal that he changed his mind, but I think they should have editted that for future editions of the books that they published, even though they could do nothing to change the orignal printed edition.

2. I only noticed a very very small handful of spelling mistakes in the books written in Japanese. The only mistakes I ever noticed was that he forgot to put the "ten ten" mark in Japanese to the spelling of a word. (I seriously only noticed this like 5 times throughout the entire series though.) For example き is "ki" and this sympol with the "ten ten" ぎ is "gi" so the proniciation and spelling is slighly off. Not a big deal at all though espiecally with how many books he wrote.

It really depends on your perspective. For example, I agree with Noon that it was a mistake for Oomori to include these things, but in your case they're not really mistakes

I think one of his big mistakes is in Volume 8. It is completely stupid to have Hestia and the others to be shocked that Bell would reject a goddess. When they fully well about Liaris Freese and his romantic feelings for Ais. Especially Hestia. He already rejected her in Volume 6. It was also stupid of her to "confess" if you can call it that in Volume 6. Because of she has known about Liaris Freese and Bell's romantic feelings for Ais since the beginning. Volume 8 should have been about Bell and Ais getting to know each other. Like them playing with the kids. Them dancing together. Instead of Hestia acting like a bitch and dragging Ais away from Bell.

1) Agree, but honestly when you are reading a LN based on a fictional world is 90% sure that the main character is gonna be sorrounded by girls who are in love with him, regardless of the guy having a clear romantic interest or even a girlfriend.

2)Again, I agree. Even more, Ais character development is relegated to SO but Oomori himself stated that you don't need to read SO to understand the series (correctme if I'm wrong here). Having a main character developed in a 'non-compulsory' series seems weird.

3) Haven't read SO 12 yet, so I can't really answer you here ;)

4&5)I think that Oomori is not very good planning ahead, and sometimes he just writes as it goes without really thinking in the long term consecuences of his decisions. That's why OEBD keeps getting stronger and stronger by indirect means, because people who fought it is being revealed to be crazy strong according with the world rules. This leads to a lot of situations being solved by the old and good plot armor

Just to add a mistake myself (and of course this is my personal pov), I feel that magic in danmachi is pretty... boring. Or bad implemented, or whatever you want to call it. Wizards are only suppose to know around 3 spells, the strength of the spell tied to the length of the chanting and some abilities (like Mage). Chantig while fighting or moving is suppose to be really difficult. The thing is that this doesn't really help to make magic users interesting, and that's why every relevant character who uses magic has some kind of 'cheat'. Riveria can cast 9 spells. Lefiya can copy elven magic. Ryuu has magic almost as strong as a mage's (implicitely stated in Danmemo) but she still can cast the spell while fighting... and so on.

If I were to agree with your definition of mistakes though, I think the fact that Oomori added Lefiya into the seires was his biggest mistake personally.

Definitely.

And another one: I don't like that Ais is too much emotionless in main series,after that I read sword oratoria it's like entirely different person (you guys might not agree thou)

1.I don't like the harem. I honestly don't really see where it would be in a hero's story. Just a mess. If it's done well and not with many women. Then it works. But lately, there are few good stories without a harem.

You have to know how to write well and without big breasts and a big ass can be an good story. But he has to be a good writer. I'm tired of this nonsense Honestly, I may like old stories / anime more. Because not have this big shit harem and many nonsense stupid women.

2.Agree. But Hestia is very much loved in this series of more important things because she is a harmonious with big breasts

3.I very much agree with you

4/5I knew from the beginning that the black dragon is the ultimate monster. So I understood that both Albert and the family of Zeus and Hera should have been very strong. Much stronger than today's adventurers.

I have no problem that the author brings the future characters in the story into play. But he exaggerated with the power of Alfia and Zald. They had to be much weaker. Otherwise it is not clear why they did not fight the dragon. Of course, they can be called traitors or cowards. But they are still exaggerated.

Do you think the author's editors gave him too much free rein on his work without some sort of limit or check?

Mistakes

1. I think the author of Bleach never intnded for people to ship Rukia. . . The truth is, we fans love to see where an attraction might go. We pick WIFUs and Best Girls. Even if this is the piublisher meddling, it will give this series more readership and longevity. As such, its hard to call this a mistake.

2. Delaying the Ais relationship has been mentioned as going against the author's originsl vision. That stong tension of what we want to see and anticipating when it might happen is perhaps the classic element to sales. It will intersting to see if the author can transfer that tension to the 3rd calamity (and give us the relationship ealry) or if the author couples the two events. Namely, Eis and Bell become a couple as they defeat the Black Drsagon. We shsall see.

3. I have posted a few defenses of SO12, only to have them deleted. Let me just say that I thought the writing for that book was excellent and perfectly relevant to the buildup.

4. Power creep in many series is pretty bad. Its a natrual way of raising the stakes beyond previous accomplishments.I think Oomori handles it well. His character power is determined by the capabilities of their foes. Age of Heroes - lots of strong foes. Age of the Gods - one hero.

5. Yet for all of his power, Albert was unequel to the task at hand. Should Bell accomplish this feat, it would set his place in the pantheon of heroes. And this is a story of a hero. . .