Parmandur
Book-Friend, he/him
I believe it.
The cantrip attack is pretty bad, all things considered. It's good if you gave it to a spellcaster but as a monk, you already can do 1d6+dex damage at 20ft range. The only time it's better is if you're using your (at this point limited) ki to do a psuedo-flurry. Ranged attacks at short range like 30 is worse than melee anyways since the enemy merely needs to prone himself. You also cannot do a BA unarmed strike after the sun soul, so you'd definitely need to use your Ki to exceed the standard monk capabilities.
Even at 6th level where the sun soul gets their BA burning hands, the 4-elemonk should have graduated from that and gotten a wider breadth of options.
Sun soul met the expectations of it's fans but I don't think it can be considered superior solely on popularity (unless the discussion is a popularity contest).
Practically speaking, the lack of an effective ranged option that uses the Martial Arts die has been a problem that crops up frequently for Monks who aren't Sun Soul. Creatures flying 30 feet in the air can't be punched, nor go prone.
Class design is about two things: math and popularity. The math in both these Subclasses isn't a problem, so yeah, popularity is the entire name of the game.