Yes, and if they're going to do a "Common Sign Language" why not do a Dwarvish Sign Language and an Elvish Sign Language and so on? Just like how there's American Sign Language, French Sign Language, NZ Sign Language, and so on in the real world. It feels kind of tokenistic to have just one sign language.
As for Draconic being the language of magic - I don't mind it, but I can see your point of view too. There are many different kinds of magic, not all of which would have come from dragons, so yeah, maybe magic needs its own language too.