It's sad. Had we not been force-fed the pile of irrelevant single-player extras, who knows what the roster would've been like.
No, we know what the roaster could have been.
Dr.Mario
Mewtwo
Roy
Dixie Kong
Plusle and Minun
Toon Zelda
Toon Sheik
These were the characters who had small amounts of data stored on the disk because they were planned and then cut. Meaning if Sakurai was able to get all the characters he wanted to in the game, THESE would have been the final 7 characters.
And when I see that list, I'd take a single player mode over those characters any day. Now I'd have liked them to keep Mewtwo, and Dixie and Plusle/Minun would have been interesting but getting a massively improved single player mode is a much better trade off then what would have been mostly clones anyway.
Now if Ridley, Geno and Megaman were on that list I might be on your side. But according to the disk, Ridley was never planned on being playable and Geno and Megaman were never even planed on being in the game so the single player didn't effect their chances at all since they had none to begin with.