Yeah that video certainly demonstrates how freaking wonderful and tactical it is to have control over the reactions and similar things (such as when to apply smite and such) in fights. It adds immersion, player agency, control and options. I just see *no* downsides with it. Some might argue it's annoying with popups but I am sure there are other ways to implement those things without it being intrusive and still offering the options it does.
I agree with you, but someone on Reddit found footage from Larian Lead Game Designer, Nick Pechenin, who stated during a Q&A video that the Solasta-style reactions would not flow well in their game and they decided against doing it.
And that came directly from his mouth before EA was released to the public. Now, they may have changed their mind since then (doubt it) after seeing all the feedback and comparisons. But as I said before, I have already prepared not to be able to use reactions in BG3 the way they function in Solasta.