This 100%I don't mind the Genichiro warmup at all. If you're not obliterating him easily then it's a sign to take a break and come back later since you're tilted.
What's funny is the first time I beat Isshin I actually died to Geni via fatigue/brain fart/not paying enough attention.
I decided to revive and keep going, and proceded to no-hit Geni and the first two Isshin phases. Isshin couldn't touch me until an accidental dodge put me in harm's way.
I later went on to beat the game through NG+7 with a variety of charmless and/or bell demon runs thrown in. Peak, peak From.