Well you're definitely not in the minority when you say that you think Robin needs a speed buff, but you'll probably find a lack of that opinion over here.
The reason why is because from a balancing perspective, it makes sense for Robin to be as slow as they are. Their moves are fairly powerful, and surprisingly quick. Their projectiles are also very strong. It makes sense that they would be lacking in overall mobility as a result; we don't want people to be able to run circles around their opponent barraging them with various spells, do we? Yes, it doesn't make sense that their design in Sm4sh partially ignorant of Robin's potential in Awakening, but this definitely isn't the first time a smash character has been changed from their source material (I'm looking at you, Ganondorf).
Robin's speed isn't particularly a hindrance either, unlike Mewtwo. Robin doesn't need to move fast to do what they're supposed to do. There's a fundamental difference in the design philosophy between Mewtwo and Robin. Mewtwo is a glass cannon character, Robin is not. Mewtwo's previously low speed made just being in a match against certain characters dangerous because of his light weight. People could outspeed Mewtwo and kill him before he could weave out of harm's way. Robin is a character that relies on projectiles to apply pressure from a distance, and their inability to escape a faster(or every) character is the reward which the opponent is granted for getting past said projectiles. This is why Mewtwo got his speed buffed twice and Robin's speed hasn't been touched since launch.
For the sake of not turning this into a thread solely about Robin's speed issues, what does anyone reading this think about Robin being buffed? What should be buffed? Should anything be buffed? Should anything be nerfed? (pls no) What does everyone think about Robin being changed? What needs to happen to break Robin's "low-mid tier" stigma?