So New SMN is a hot button issue but most people are discussing the mobility, aesthetic, and Damage.

While those things are important. There are some legitimate mechanical issues with the job. The most annoying is Rekindle and Summon - Demi ruins your rotation if you die.
Because Deathflare does damage, Rekindle is basically you losing 500 potency every other minute. at level 69, SMN actually feels better because you get deathflare once a minute as opposed just every 2. The issue however becomes when you die.

If you die, Summon Pheonix will revert back to Summon Bahamut which means Deathflare will no longer line up with the bigger raid buffs as Bahamut will now be on the even numbered windows as opposed to the odd number where the 2 minutes like searing light go out. This is incredibly frustrating for picking up where you left off and i'd argue it could be detrimental in prog where your death is already detrimental. This would be like a Red Mage dying and now they can only use manafication on min 2,4,6.. as opposed to1, 3, 5 like 2 mins normally work. Bahamut is SMN's biggest DPS window so it being displaced is frustrating.

In addition to that, because Bahamut is a spell, it's effected by spell speed. This mean it will naturally desync itself from searing light. This is frustrating too, it breaks the rotation flow when i have to sit on carbi and ruin 3 when the job does nothing to incentivize doing so besides waiting for buffs. I'd appreciate it if Summon demi was a Ability so that this doesn't happen.

These aren't big issues, although i'd argue the former makes recovery alot worse since death permanently ruins your burst window until you die again.