The primary reason I don't miss Stormblood Summoner is because the lockouts and oGCD Wyrmwaves forced you to hold and burn cooldowns in a terrible manner to accommodate a shoddily designed but mathematically necessary rotation. It felt like pure developer hatred for the way Heavensward tore up their terrible idea for DWT and Aethertrail. The only class with a worse rotation than it from a design standpoint was Machinist. Current Summoner isn't even remotely close to that. It also isn't nearly as punishing. There is no difference between Phoenix and Bahamut numerically or mechanically. Their actual differences lie in Trances, where DWT is 400 potency less than FBT once you do the math, plus the cast time differences; I believe potency difference is even less on AoE (Outburst is good). Sure, you're encouraged to save Ruin IVs for Bahamut, but it is not a big deal. Using Ruin II to get the wyrmwaves right is still a DPS gain, and only matters for the last two to three GCDs you use during Bahamut. Tri-Disaster and Devotion work exactly the same as they did in Stormblood. I dislike both for the same reasons I hated Summoner in Stormblood. Same issues. Lesser Degree.
Overall, moving away from what remains of Stormblood's bad decisions, merging stuff down, and bringing back Aetherflow so Trance can be flexed again solves every issue we have. Do that and Summoner doesn't need any more major changes in its rotation. It just needs pets to function properly.