Ex trials aren't meant to be easy, they're at least easier than savage raids, but definitely is not something you should expect to clear in 1-2 hours with random DF people. Sophia ex may be considered easy, if you compare them to other ex trials in the past (when they were new). Mechanically it's not the easiest but it's a lot more forgiving to mistakes and low dps.
Some people take days, even weeks to clear ex trials (it took me a month to clear thordan ex back then without a static), I think you're just having wrong expectations since this is your first difficult fight. It's normal to take many hours before you understand all the mechanics and clear it. If you compare sophia to other ex trials in the past, yes it's one of the easiest, but if you never did savage or ex trials before, it is still considerably harder than normal trials, dungeons, mhach raids, and alexander normal mode.
Mechanically sephirot is simpler than sophia I think, but it's also a lot more punishing to mistakes and deaths. My first sophia ex clear had 16 deaths, every single member in my party died at least once, and we didn't get to enrage. I'm quite sure that's not something you'll see with any other ex trial before this.
As for the tank buster, there are several similar cases, notably perpetual ray in a8s and chastening heat in a12s (both of which also give vuln up to the tank receiving it, thus requiring tank swaps). For this kind of tank busters the co-tank must provoke during the cast.
