As has been mentioned, using KotR on Jenova increases Safer Sephiroth's difficulty. And VeloZ, it is correct that if you're at level 99 the difficulty makes a significant jump as well. If you were lower-leveled and did not use KotR, you'd probably find him very easy.

I don't think he was particularly epic. He is at least moderately difficult at level 99 and after using KotR, but still not that much. The final bosses in FFs aren't really that difficult for me, but I like to do a lot of things in games and not just rush through. Some of the optional bosses have certainly been challenging, though.