I think using humans can make sense because:

1) like you said they aren’t fantastic themselves and of course are the most relatable to the player — so they’re a stand-in for the player exploring a strange unknown world, and THAT is where the opportunity for wonder and the fantastic will come in.

2) whatever races are common in the world could potentially lose the fantastic feel through overexposure. or if there are an endless number of races constantly interacting with (or part of) the party then there’s the danger that nothing will feel fantastic. (In the extreme case it could feel like each race is just and expression of different combinations of the character mechanics present in the game.)