With the caveat that I only played PnP D&D in the 1970s and 1980s, I don't think either TB or RT really capture the tabletop ideal.
To do that you would pause at the start of a combat round, wait for all actors to enter their orders ( so it works with either single or multi-player ) then run the round with all 5e reactions being offered as they occur ( with auto-pause or maybe a temporary UI button ).
It would probably be quicker than turn-based as well as overcoming its time-serialization problem, without going to full real-time. If it were possible to restrict reactions to simple one-click activation ( again, I don't know much about 5e ) then each round could complete fully in real-time, even in multi-player.
Obviously BG3 only continues the City/Setting, not the original story; and clearly it will be using modern technology, and from what little has been said, BG3 may not be just DOS with 5e rules.
Larian do seem to be spending a lot of money on the game, so I suspect they will need to appeal to a wider audience than DOS to break even, which may also indicate significant differences to their recent games.