I'm happy he's back just for the subtle yet decisive differences between him and Mario. I was never a fan of F.L.U.D.D. either. Also, I liked his personality overall.
Actually, Dr. Mario is quite different from Mario. He has a different D-Air, slightly different Final Smash, different D-Special (thank God), a slightly different F-Smash, and I'm even hearing his U-Special functions differently. He also may still have his different F-Air, but I didn't see it yet personally. So actually, no... Dr. Mario is better than Young Link and Pichu combined, since neither had as many differences.
Also, as a King K. Rool / Ridley / Mewtwo supporter myself, I would have liked to see them in Sm4sh as well, but attacking other characters due to their absence isn't going to change ANYTHING; Dr. Mario is a welcome addition in my eyes. Also, Dr. Mario being a "crappy game" is just your opinion.