You are totally right when you say that in DnD classes are much more important than in BG-3 ... But you have to realize that in DnD there is no limit for party ... while in BG-3 there is ...
If you would NEED to have Rogue with you, since noone else is able to lockpick, stealth and disarm traps so effectively ... if you would NEED to have Cleric with you, since noone else is able to heal, buff you and debuff enemies so effectively ... if you would NEED to have Wizard with you, since noone else is able to cast spells from scrolls so effectively ... if you would NEED to have Fighter with you, since noone else can jump so far, handle heavy objects etc ... You allready reached your limit, no Tav for you, sorry.
What im trying to say here is that if Larian refuses to allow us to play with 6, they need to loose rules a little, since otherwise half companions remain unused forewer, since they dont fit to any specialized role.
5e isn't as role-limited as you're suggesting here. Almost any party composition is viable which is one of the best things about the edition - the classic Figher+Wizard+Cleric+Rogue (+ Bard if 5 players) adventuring party isn't required.
Any class can lockpick in 5e if they take the thieves tools proficiency through a background or feat. Although in BG3 lockpicking is currently based on Sleight of Hand, right? Which is even easier to get. (Plus, I believe the Urban Tracker Ranger in BG3 gives proficiency in thieves tools, for when/if that is implemented). And stealth is even easier - any dexterity class with proficiency in stealth can be sneaky.
You can easily replace a cleric with a druid, bard, wizard, and/or paladin. I've had many 5e parties without a cleric; the hit-dice-on-short-rest and full-hp-on-long-rest makes clerics much less necessary compared to previous editions, and these other classes can buff/debuff.
You can easily replace a wizard with a sorcerer, bard, druid, warlock, and/or the half casters. These classes can use many scrolls, some even that wizards cannot.
You can have a barbarian, paladin, or cleric with high strength and athletics proficiency to jump and lift heavy objects; no Fighter required.
The 5e system is already pretty flexible - additional class flexibility isn't needed even with a 4-person-party restriction.
So my takeaway is that these threads are largely melodramatic then.
