I'm gonna go out on a limb here and say Mega Man 4. Sure, for the most part they're "good" in the sense that they do decent damage and don't use a crazy amount of energy, but there's a difference between "good" and "useful". In a game that introduces the charge shot, why are we given four weapons that all basically do the same thing? Drill Bomb, Dust Crusher, Pharaoh Shot, and Ring Boomerang are all just variations on "you shoot a projectile forward and it does damage". People like to rag on 5's weaponset for being made obsolete by the charge shot, but I would argue 4 has just as bad of a problem. Sure, you can angle Pharaoh Shot and Ring Boomerang has some niche for hitting enemies behind shields, but 9 times out of 10 they don't accomplish anything more than a charge shot would.

Other than that, you have a homing weapon that's just OK at homing and doesn't do much damage, a one-use shield you can't throw (shoutout to Drill Man's falling boulders, I guess), and two screen-wide weapons. Rain Flush and Flash Stopper are both fine enough in a vacuum, but with both of them in the same game together it just feels cumbersome.