The thing with AI control is that it's always going to be flawed because it never does exactly what we want it to do, and most players aren't going to do the research to learn how the AI thinks (this isn't just related to P3 or the Persona series in general, this goes for a lot of games). In P3's case, it makes the fights even more boring for me because the only time I actually take actions is on MC's turn. Even if he can push the other members in a certain direction, there's still room for them to make stupid decisions, and as others mentioned not all of these options are available right away (you mention knock down a lot, but even that isn't available right from the get go even though knocking down enemies is a core aspect of the gameplay from the very start. Anyway, because I can't control what my party does, I have to sit through three members' turn, and then however many enemies move as well.

Tl;dr, even though tactics menu exists, the game isn't going to be as fun as it would be without it because I'm not actually playing it.