X is a comfortable challenge if you walk along without stopping to level grind. If you spend any time mucking about, it can become too easy (not that I really mind one-hit kills or that Stonestrike blitzball you can buy from O'aka right before Operation Mi'ihen.)

I always waste enough time wandering along side passages to pick up various goodies, so that Lulu has Thundara by Operation Mi'ihen and can handily take out one arm per spell with that bug boss thing. If you don't have her and Auron lopping off one arm apiece in a single turn whenever the arms regenerate, that battle can take a while.