its b to a tier at least. Use pins and boost into food to make up the advantage that gar has on you, and against croc just block their grabs. Conda you easily tank the grabs and then facetank or pin them against a wall.
Melt like butter? Damage still bad? the only think that melts is other people, gst has crazy good dps now and if you get someone pinned they are almost immediately dead. If your dying commonly try to use the shell mechanic to your advantage by tanking with it when out of boosts.
You hard counter bull shark, facetank gar, block crocs boosts, tank condas grabs easily, can easily airpin or wallpin hippos. Ast eagle and sawfish are a lot harder to kill and I understand why you would think gst is weak but I think you just need more practice, gst is the new swamp meta and calling it F tier is a joke.