For the concern of lower level summons and having to figure out an egi form for them, there are already egi forms for Ramuh (they're used in his fight), and it's easy to just recolor current egi's or use current in-game models (like the water/ice sprites for Levi/Shiva). However, the easiest and most logical answer to this is, don't put those summons at lower level and keep the current rotation as it is - just add the higher level summons after 90 / 100. There's no need to include Shiva / Levi / Ramuh before the level they would be the full primal forms.

I don't want to go on and on about this, but it truly does seem the only way to enact change with the devs is to make the most noise. Seeing as how they still haven't fixed the limited races, they still haven't come up with a better rotation for healers, they still haven't addressed many more very valid gameplay criticisms after years of complaints, and on top of that they definitely don't seem to implement the complaints that are just passively given; it does kinda seem squeaky wheel gets the oil sort of situation.