If clones can provide different playstyles regardless of their similar movesets, what's the problem?
Both Doctor Mario and Falco in Melee were much more interesting and well designed than the majority of the characters in the same game, and despite looking identical I've played the game enough and watched a lot of tournament plays to tell you that yes, they're different enough. There's also other characters like Young Link that have showed much more potential than Regular Link with his keepaway game, even showing that he can counter a top tier (Jigglypuff) whereas Link can't. Also, every Marth player will tell you Roy is super different.
Granted, they're basically the same exact concept of the original characters they took from but executed different, but if they can add to the metagame and provide better match ups then what IS the issue? Especially since they don't take up a lot of resources, so if anything, consider them freebies, not waste of slots. Sakurai said himself that 6 clones took less work than one original character (who, in Melee, was supposed to be King Dedede), and half of those clones ended up fan favorites in the Smash scene. The only stinkers were Pichu and Roy.
Personally, I main Doctor Mario in Melee, but I don't like using Mario because the subtle changes do make all the differences. Doc allows me to rush head on first and kill quick, Mario doesn't.