Eh for several reasons I still do not think adding the other three summons will actually improve the job, aesthetically or mechanically. I think, for at least as long as we have strict 2-minute rotations, it has all the summons it needs to feel like it has a base kit and some extra powerful spells; anything more would actually dilute the "summoner" feel imo (Solar Bahamut is already kind of doing this), as none of the base kit summons would be around long enough to feel consequential. Any notions of introducing the concept of "choice" like how SMN has been represented in every FF game prior, is just ignoring the reality that FFXIV is not designed to accommodate a traditional iteration of SMN.

THAT said, the obvious and elegant solution is just to implement glamours. That would provide plenty of player choice without affecting the job design.