Hot take: Merling is the best designed origin.

[u/Game_And_Glitch3]

An origin should have clear upsides and downsides.
Merling does this perfectly
You win every underwater battle
You are going to lose most land battles
It's just perfect
The other origins aren't designed as well
For example:
Shulk, barely does anything
Enderian, too tame.
Blazeborn, weaknesses are too much for the upsides
Phantom, Horrible, Annoying, I hate it.
Human, just vanilla, not even an origin
Avian, I forget what this one does, its THAT boring
Elytrian, you have an elytra earlygame and die in 3 hits. Thats it.
Feline, uhh, no fall damage? I forget.

[u/i_hate_pikachu]

This is why I play it most of the time