It's 9 but a bit worse and has notably worse weapons but 9 is still the best one so that's like saying 23 karat gold is worse than 24 karat and like yeah it is but also it's still fantastic
Water shield is a very fun weapon but this is sadly another game where one weapon is just like the best one because Blade Man's weapon exists (sorry forgot the name I'm writing this at 1am) Solar Man's theme is super good too I love that song
Also having the gameboy bosses with their weapons as DLC and fully playable Proto man and Bass is insanely cool and makes this one of the most replayable games in the series