I followed the SF games extensively I can confirm this version of Seth is not as hard as Vanilla Street Fighter IV. His first round form (similar to Rugal from KOF) is always easier but they turn the difficulty up to 10 on Round 2. You can't cheese him you have to systematically exploit holes in the AI's offense to beat him. Still he wasn't as hard as KOF bosses but he was a pain then. USFIV lowered his difficulty a bit taking away a bit of the randomness unless you raise the difficulty. Shin Akuma, Shin Goken, Evil Ryu and for Christ sake Oni are the real controller tossers.

There are secret-true boss battles of Akuma, Gouken, Evil Ryu and Oni in this game. Do them too. :)

didn't they supposedly make him easier in the ultra version of street fighter IV?

Here's hoping you face the Extra Bosses one day...