how good is gorgon? or why i should avoid her?

Gorgon is an permament avenger so yeah to anyone who dosent have jalter
Also she has an aoe np wich could be good if there is ever multiple rulers in a node

Gorgon is gud and she's story locked, so you can't roll her outside of banner. There's little reason to not go for her if you like her, she's one of the best 4* servants.

If anything, the other AoE Avenger, Edmond Dantes will be a much better option later on.

So yeah, Gorgon is far easier to get and run since everyone will have Merlin on support (you don't need your own Merlin at all). While Dantes will be the best offensive unit of the game but he's hard to obtain and double Skadi is key on his staple team setup.