[quote=@Sanity43217]
<Snipped quote by Mirandae>

I only ask because a Bahamut Regalia might not want to turn into a 85 foot dragon. In scenarios like fighting in an office building it might get cramped to get so big, for example. 
[/quote]

Indeed what Aeolian said: your character can use magic native to their Dominant without Crystals. But, yes, the size of the Dominants do offer some interesting narrative situations.