They could and more likely did start with raw 5e implementation in prototype. And it's not something that normally goes into final product.
They have never shown any evidence of that. I find it unlikely since the first gameplay showcase looked like a DOS mod and to me was a disaster.
So they implemented 5e raw -> just to step back and make a D&D/DOS hybrid -> just to step back and make it more like D&D but missing many core features?
Doesn't make any sense to me.
The very first versions of BG3 was to far offmark from real DnD rules for my taste, but patch 5 have made great changes. No more does food heal in combat. Food is used for resting though. Well and then no longer it is easy to push opponents you need high strength for that so some dex based rogues will not pull of it. In addition opponent weight does count now so so if this game will have Giants I doubt you can push them.
You can not anymore jump away from opponents without causing an attack of opportunity. You can now use disengage to move away, but then you forfeit any chance to attack opponent as in real Dnd Rules. All this after patch 5 at least and enemy AI is smarter then before at least. Companions attitudes are tiny bit less hostile then before towards players.
I have been told on forums that later likely in Act 2 will be introduced good alignment companions.
Personally in Solasta I got super annoyed by somatic component need in spellcasting and immediately disabled it from settings.
I have played lots of Dungeons Dragons pen and paper with more then one GM and somatic component has not been a huge issue in those sessions combat is fluid.
With Solasta default settings when you choose most close to real Dnd rules my Wizard could not even cast Mage Armor when holding something in the hands. If I would meet a GM with so strict settings as Solasta default desktop settings when you choose most close to real DnD rules and top of that make somatic componet fix a slow process I would say sorry you can not be my GM and I quit playing DnD with you as GM. Well and those GM that I have played with has allowed me to as free action I say drop this item to get hand free and I dont need use some annoying interface to do it. GM has always made it fast and fluid thing for me. It takes less then 3 seconds with a fluid GM to understand I have hand free in real Pen and Paper if I say I drop this item and cast this spell.
Well and many friendly GM in pen and paper has been less strict about somatic component and do not even care if player do not have hand free when casting spells.