Ruby Weapon was a bazillion times harder than Emerald.
I took down Emerald without using any Summons and without Underwater materia. =/
Also, Omega weapon was a total wuss if you knew his pattern and when to use Defend. Sure, he could still instant nuke your party if you were unlucky, but that can happen with all of these super bosses (one time when I tried to show off my Emerald ownage I got double Aire Tam Stormed - while only two characters died, I couldn't recover fast enough).
And Ozma was a bitch. That fight was like 90% luck. =/ One of my hundred or so Ozma attempts, he literally did nothing but Curse. -_-;