SSB had a reason to remove the characters though.
Dr Mario - He was just the EXACT clone of Mario so they could've removed him anytime. Though I can see how ppl are mad about it. Afterall he was my main in SSBM lol.
MewTwo - They removed him and replaced him with Lucario, I don't know if you notice it but Lucarios moves are almost exactly like Mewtwo's
Roy - He was replaced with Ike because they have thee exact moveset. So no harm done their
Pichu - He was just a more destructive version of Pikachu. He was just their for his cuteness.
Young Link - He was replaced with Toon Link. They always replace Link with some alternate version of himself. Which I like
SSB mostly replaced those characters with someone who's exactly like them. Their was no harm done when they did that because if you liked Roy you could probably be Ike, and if you liked Mewtwo you would probably like Lucario.