Which part of summoner's rotation am I meant to find satisfying?

[Dyvid]

I played FFXI summoner and it was pretty much like the way XIV summoner is now. It was impossible to actually maintain a summon other than carbuncle. You summoned x for y benefit and switched back to Carb.

No it most certainly does not. FFXI pets couldn't stay out because of developer made it consume massive amount of MP, not because of some spaghetti code. Even in the early days of FFXI you never kept Carby out because the Damage to MP cost ratio didn't justify the downtime which is why most SMN was SMN/WHM who mainly healed with occasional Summon to mitigate damage, (Stoneskin, Aerial Armor, Fenrir Roar). It was a sad joke.

The fact that we are still actively discussing SMN even after this redesign was supposed to "fix" the job just shows how much of a failure it was.