I'd like to agree with you (especially on the part about there are not character slot), but I can't, not completely at least.
There were character refered only as alternate cstumes/color schemes in the past, like Daisy, and I'm sure that before Brawl, even Wario was refered by that Mario's color scheme.
It's happening again (Dark Pit), and they don't have to match completely the character, because they're just references.
My problem with Waddle Dee are: you're right about them having no fighting experience outside from the spear, and that's bad in my opinion, I don't want another Little Mac with spear instead of punches.
And, there are lots of better and more promitent characters from the Kirby franchise that could offer funnier gameplay and more unique special moves.
About the character slots. There are no character slots virtually, but in fact there are. The character select screen is designed so each player can select his character at the same time, so the whole roster has to appear in one single screen with understandable character icons and texts (at least, on WiiU). I did a roster prediction of 59 characters (+ random, 12x5=60 icons) and I tried to put it over the demo character select screen to see how it would look, and it's already very hard to understand what's written in the icons... the hand with the token is as big as 2 icons, so I thnk that they're already too many. In the character prediction, there were just 11 newcomers (they were 9 at first, but I added 2 for a better look of the screen, to be able to make the 12x5 table), and they are 1 newcomer for each big franchise (with small excceptions). It's obvious that there is a problem of quantity related to the character selection screen, unless they redesign it completely.