For the primals, I don't think any of them are particularly difficult. Titan isn't hard. People's internet just isn't suitable for it. Ramuh is okay in terms of difficulty for the primals to me. Primals aren't difficult, but Ramuh encompassed awareness, DPS, communication... more interesting concepts of difficulty. As for the coils, Turn 9 is definitely harder than T10-12. I've only been to second phase in T13 (left group), but was told it is more of a dance than fight.

Would rather have RNG in the fights over remembering a phases mechanics.
T7 was once difficult(SMN Kiting) because of Renaud RNG spawn. Sometimes I was able to place the renaud before the subsequent Voice/Shreik, while other times I had to kite through both. That type of mechanic RNG needs to be placed on ALL members of the party. Tanks shouldn't just have to focus on cooldown management, tank swaps and limited movement mechanics. DPS shouldn't only have to worry about movement mechanics.