I found 8's weapons to be pretty useful.
Even the Mega Ball could be used to high jump before you get Tornado Hold. (or as the alternative when you dont want to waste the ammo on TH, like in Astro Man's maze)
Astro Crush was the only one I found to have limited use due to it's low ammo count, but its a good screen clearer.
And 8 is the one with not just the charge shot, but 3 different Charge shots.
The crappier the Special Weapons, the more the power of the charge shot will make you want to use them even less.
But if they are crappy, I wouldnt use them anyway. Id stick to the default buster or the better weapons. Like Shadow Blade and Spark in 3.
Fact of the matter is, the more abilities Rock gets by default, the better the Special Weapons have to be to outshine that base.
And whats wrong with that? Thats like Inti creates making Hard mode hard by nerfing Zero's default abilities rather than actually making things harder by making everything else faster and stronger. Its making them more useful by nerfing the player. That shouldnt be needed. 7 and 8's arsenals are good enough even with the Charge Shot. Even MM&B's weapons, while not always useful, were made useful by the game's broken difficulty as Rock.