Are you going on just difficulty alone to judge this? Ifrit and Shiva EX are below the threshold of the other ARR EX Primals. If it wasn't for the ability to fall off, Levi would probably be in the same company as those two fights, too. I would say the order of difficulty for them was Titan EX -> Garuda EX -> Ramuh EX -> Leviathan EX -> Ifrit EX - > Shiva EX. Also for its time Ultima HM was harder than Shiva EX was. Ravana EX is harder than Shiva EX and Ifrit EX. And you have to remember DPS weren't crushing Ifrit EX back in the day, so that whole triggering enrage wasn't a thing. Healing was much easier because damage came out in slow bursts rather than a Michael Bay extravaganza that the final nail phase became towards the end of ARR. The only difficulty of Ifrit EX was getting the healers/party on the same page for where to go with Searing Wind/Nail direction. I cleared it in Duty Finder after 3 lockouts with randoms back during the days when people were helpful in this game. Compared to Garuda and Titan which took...a lot of time in party finder groups...
Yea, latency was a killer in Titan EX, but as scripted as it was, it was the longest set of mechanics to memorize at the time (other than T5). And despite being scripted, there was enough RNG stuff that made it a nightmare. The HP check was real with the gear available, and despite it being a scripted fight, the bomb formations in the final phase + where you baited Landslide or Weights caused a lot of people trouble. Remember, this was at a point that anyone other than a tank getting clipped by Weight of the Land or a bomb going off meant you died. For some reason DPS check at the heart was an issue for a lot of groups I went in with, but the single hardest part for almost everyone was the adds + bombs + landslide. Trying to kill the adds in the right spot + dodging multiple aoes + trying to dps or heal ended many an attempt. And back then, you got to deal with that stuff twice. I remember actually seeing enrage in that fight a few times. Also you had to actually tank swap.