Yeah sure, if you practice how to cheese then it works wonders.
But the spin attack was purposely made very hard to keep on stage 6. Most place you need to jump have alternating power ups that you auto hit if you jump slash, which replace jump slash with a generic ninja star
even so, each boss you defeat, you lose your spirit and weapon. So you face the next boss with 0 specials.
beat the masked devil? Great. Now fight jaquio with no special.
Lose and get kicked back to 6-1.
Beat jaquio after coming back? Great. Now face the demon with no special and no spirit.
Lose, get kicked back to 6-1.
Part 2, the bosses are arguably easier. There is no huge long kickback to redo all of the final stage and the enemy spawn is way fairer.
Every retro gamer stream who played the ninja gaiden nes games from scratch spent hours on 6-2 and flew into shock when they lost the first fight with the masked devil and got kicked back lol. But when they played ninja gaiden 2, they comment on how much easier it is and beat it way faster than the 3 or 4 videos it took for NG 1