I mean, really, as I've said before in the most practical and pragmatic terms, a proper reaction system will save more time by letting you directly control that counterspell against that fireball (or that fire bolt cantrip going for that barrel next to you) that's otherwise going to wipe your party and force you to reload the game, more than any popup could ever hope to waste.
Too many people think of the immediate, but a truly well designed turn-based game must account for the long term.
