Nope, not cheating at all. Last night, I decided to fight Nemesis because I was bored. Used my 'dream team' of highest-stat characters. It went something like this: Hastega, Auto-Life on everyone, Quick Hits, annihilation of party members (either all at once, or one by one), repeat.
It took a good couple of hours to win. If I'd used Zanmato, it would've been over in moments. Either way, I know I'm strong enough to win. Zanmato is just the pragmatic approach for the time-savers among us.