Ghast
The ghast origin is very underwhelming in many ways.

Power(s)
All his powers really.

Balance Suggestion
Double down on his fragility, making him a more ranged dude. Most of the time the fireball misses, and, if it hits, it deals like half damage. More damage and less cooldown maybe.
The fly and the pass through blocks are very cool, but maybe make you being able to use your pass through atleast, a bit, in the overworld. Also a bit more control on the fly.
And now, the worst thing about this origin: the hunger. WHY I'M SO HUNGRY DUDE? I'M ALWAYS MUNCHING ON FOOD. Fix it, please (May be a bug cause the hunger is not on the wiki but yeah).
Thanks for the datapack regardless!! The native spawn on the nether is great challenge and the skills are very wellcoming, if i WERENT HUNGRY ALL THE TIME lmao.

The Ghast seems to be Bugged with it's hunger. It's hunger is constantly drained even if it stays still. Given how this isn't listed in it's origin, thematically makes sense, or makes any game balance sense; it's definitely a bug that needs fixing.
I just installed the minimum mods required for the Fabric Version of 2.2 Origins++ and Ghast has this issue.
Edit: At least on Version 1.19.3.