Because a small deformed egi makes more sense than a tiny mini-primal and looks less goofy. I know you want full size like Akiza but it's not happening

And comparing XI to XIV, just look at the gameplay. In XI you do everything from the menus and you can literally stand still for the entire fight because of how the game works, so giving you a huge ass summon or a little ball of yellow makes no functional difference.
In XIV we have to actively dodge shit, position, deal with mechanics and all sorts of crap. If we were like XI summoners we'd either die constantly ourselves trying to do shit or the primals would just die when we can't move them in time. See: Using Ifrit in any end game fight. And if we were built like XI summoners we'd be useless as shit as soon as the primal dies. And with the mechanics in new coil and assuming any future stuff isn't going to be similar or worse, anyone bitching for SMN to be heavily changed to be like it is in XI or some other game is an idiot imo.