I didn't know anything about this character or her outfit history, and after doing a Google image search, yeah, I agree with you about the bikini. Since characters wear bikinis on kids' cartoon shows all the time, then obviously showing skin isn't in itself necessarily a problem for the "family-friendly" set - so why did they have to alter the Starfire outfit so much for TV? So that tells me that yes, they weren't looking for any old skin-showing outfit. Otherwise she'd just wear a bikini. This one's fanservice any way I look at it.

Apologies if I've gotten anything wrong about the various iterations of the character.