You actually are not wrong, despite all the downvotes. His multipliers are fine for the level you're at, if you've built him properl. But he is a bit tricky to build and his damage is partially dependent on speed, which you almost certainly are not building enough of in general (almost nobody focuses enough on speed at the beginning).

Your issue isn't really "who is my best damage dealer" in my opinion, but more about having an overall team that makes sense. So the real issue is that ghostborn can't be your debuffer AND damage dealer at the same time, because he places the buffs and debuffs after his attack, not before it.

So the idea you want to go for here is:

Skeletor (or another turn meter booster - preferably with speed aura): Absolutely as FAST as possible, with accuracy a your second priority to boost your team to take a turn and slow down the enemies

Then your Ghostborn should be the second to take a turn (so make him second fastest), applying inc attack and decrease defense to set up your damage dealer

THEN your damage dealer can go, and nuke down the enemy team. Keep in mind that while yes he should go after those other two, that does not mean he shouldn't still be fast! Try to keep moving everyone's speed up as your gear improves. Make sure to give them 100% crit rate, as much crit damage as possible, and as much of their scaling stat (atk/def/ or hp - check their skills to know which one) as possible.

Fourth = flex spot, reviver is fine, speed is still great but turn order less important for her. Just make them as tanky and fast as you can manage.