Positive things first, I like that Delibird idea.
I suggest making Levitate innate, so you can give the Levitators additional abilities, as well as add Levitate to more Pokémon since it does not interfere with the current abilities of that Pokémon anymore (most notably, the Magnezone-line, but Glalie, and Munna/Musharna as well as a few other Psychic-types).
Also, how can Dragons resist Bugs because of size difference? Scolipede shits at that argument, being bigger than any non-legendary Dragon (and most other bugs aren't that small either). And even from a smaller Bug, for example, Beedrill, an attack would still hurt a dragon. Ever seen that stingers? They are about as large as a sword or pike. Even if you are a Dragon, that will hurt, especially since none of the Dragons in Pokémon is really big.
I do agree the fire STAB on Dragons does not make sense. Most dragons that are supposed to breathe fire because they can breathe highly inflammable toxins that catch fire once released in the air, but certainly not all dragons are capable of doing this. In fact, only the dragons styled after European myths can, and guess what? There is no Pokémon styled after an European dragon.