As you have played XCOM, its easiest to say that BG3 switches from RT exploration/interaction to an XCOM-like combat mode.
Like XCOM, the BG3 combat will probably be OK, but potentially rather drawn-out.
Historically, most physical games ( os opposed to sports ) have been turn based because of issues of practicality. A non-moderated game means each player needs to watch other players to ensure rules are followed, and to know what has happened.
In the physical world, it is actually quite hard to devise games that operate well in simultaneous modes. Even early computer-based games were mostly turn-based, simply because the hardware wasn't good enough to consider anything else.
From my viewpoint ( or preference, if you prefer ), games that don't operate in RT while trying to portray a RT environment/situation are less interesting. So I prefer computer-RPGs to find some way of making the game flow.
Unfortunately, it is not always possible ( not yet, anyway ) to produce an adequate mechanism for giving players control that everyone will like. Games that need to follow rules converted from physical games ( such as DnD ) can be particularly difficult, as they cannot readily choose to make wholesale rules changes to better suit the computer environment.
Fortunately, most activities other than combat in BG3 are RT, and will probably work well.
Then the best solution is to provide us with the ability to choose which mode we want. That way players who want only TB can play it that way, and the players who want RTwP can play it that way, and players who want a combination of the two can play it that way, and the players with similar preferences can team up with each other.