Dude. Plastic Man is low-key OP.
I mean, the man is quite literally made of a rubbery substance, making him basically invincible. He can bend into any shape or form he wants, literally anything. He's got superhuman strength that permits him to do shit like hold up a collapsing cave for a period of time. He can unlock any door with his powers simply by putting his hand in the lock and mimicking the shape of the key. His ONLY weakness is heat and fire because he can melt.
The ability to mold his shape into literally whatever he wants along with immunity to nearly every weapon ever made, unless you have a flamethrower handy, makes Plastic Man insanely over powered.
He could single handedly destroy entire cities if he felt like it. The Justice League should seriously be grateful that Plas is working WITH instead of AGAINST them.