That's kind of the problem with having a sizeable cast being around the main character all the time.
I disagree. If the Japanese version can do it fine, I don't see why the English version can't handle it just as well. This is a localization issue, nothing to do with the source material.
Also, as others have stated, Gladio is definitely not a brainless type character. Noctis is more humble than most standard MCs in a shonen manga as well. I don't really think you can compare the cast to the usual stereotypes to be honest.
Prompto is the comedic relief? Gladiolus is the buff but no brains guy and Ignis sounds like a Butler??? And Noctis? Typical Shonen dude but more moody? See, all this gotta be fixed with good writing.
Like I said (I'm basically repeating myself here sorry) this is not the case in the Japanese version, so really it's just on the localization team to get their act together and stop changing how characters are portrayed.
I'm really glad to see Tabata actually caring about these things, because it was one of the main problems I had with the English localization, bad voice acting is fine so long as the actual dialog and interactions are done fine, but when you change an entire character to be completely different to his Japanese version (the original true version) it just creates this huge separation between how a group of people perceive a character. What's the fucking point of making him a butler style character when that's not his job? Ignis' entire role to the Lucis line is to act as the strategist for Noctis, he's supposed to be helping Noctis through everything as his advisor, not as some personal butler that fetches his things for him who addresses him only in the highest form of respect using his noble title. Referring to Noctis as "your highness" to me says "I am below you and serve you" when that's not at all what Ignis is to Noctis.
Well, we know that they all know each other before the start of the game.
I don´t see any problem in starting the game with the whole cast being introduce from the get go.
I don't see a problem with it either, the characters can easily be introduced from the start during the opening sequence. I've seen anime/manga where the main character already knows three other people at the start and they're easily integrated into the story in a way that feels natural and without having to separate them entirely to get people acclimated.