Things you mention (like reactions) don’t come from engine limitation - it comes from Larian believing that such system wouldn’t work well in computer game and is looking for other solutions. I wouldn’t expect reaction to be implemented as they are in PnP at this point, though it’s been mentioned that they are looking on some kind of change/improvement of the current system.
It’s been also confirmed that engine have been heavily overhauled for BG3 - they are not limited by what D:OS2 allowed, and that should be obvious just by comparing both titles.
