He won't because that's not his style

True, but it could theoretically be the strongest spell ever, because magic strength is based on chant length & Argonaut boosts things more the longer it is charged.

I think he cant do that correct me if i am wrong but bell has to concetrete while charging argonaut and to chant a spell i dont think even somebody of riverias could do that also i dont think he can do both at the same time even if he did have a spell and argonaut.

Even if Bell had long chant spell like that I don't think he could do it. Concurent chanting requires a lot of focus from mage just like charging Argonaut does. Focus that much on both things might be nearly impossible

He's done the impossible before. Plus Nearly impossible isn't truly impossible, only improbable.

I think if author does it ,it would not be a very long chant,maybe like alfia's magic.

And I also think it can be done since he is the MC and also alfia's nephew, author didn't think of alfia before ,so I think with this new introduction (I mean her relationship to MC),maybe author can exploit it to justify bell being able to do it.

I mean I don't think it has do with her curse but just her talent.

The point of concurrent chanting is for mages to be able to fight against enemies on their own/more offensively than standing behind shields and such. Unless Bell gains a magic that has a long to super long chant (which is highly unlikely), he has no need for it. You wouldn't need concurrent chanting for Alfia's first two magic