Calling Terra vs MF hard is like calling Chocobo Racing in FFX hard.
It's not 'hard' that's the problem.
Yeah, it isn't "hard" in a skills sense. At least not completely, it still takes some practice and skill. It's hard because of how lucky you need to be since his attacks are totally random. I got to the point where I was able to get him down to half health on almost every attempt but then he'd use those unavoidable orbs or just get a lucky shot in while invisible.
It's funny since its such an absurd fight yet you can still pretty much beat him at any level if you're lucky enough and have the right abilities (attack/magic haste, curagas, thunder surge).