It depends on which version you are playing.
NA Nemesis, or Int. Nemesis and Penance (North America/International)
Nemesis would probably seem less difficult, because it is just on your stepping block to fight Penance, has less HP, has less damaging attacks, and only has one opponent. Penance has three, but accordding to you, your stats were nearly double when fighting Nemesis and then fighting Penance. Not only that, Zanmato costs are less than 1/2 of that in the NA version.
Now, if this were NA Nemsis, while the stats are exactly the same, the NA version does not have nearly as many level-up-aids, nor does it have Ribbon, which prevents you from getting the ever useful Confusion/Berserk/Poison. There are so many player-friendly lackings in NA, that Int. altogether is easier.

I found Nemesis harder as well.
Too bad I was playing the non-wussy version.
I don't care if you live in Europe and Int. is your only option...