Also Data has no apparent power source, so he must literally create energy out of nothing, defying the law of physics.
And he's made of metals, and thus should weigh much more than a human of the same volume whose density is comparable to that of water, but does not. But if he really is the same weight as humans he shouldn't have super strength, but he does.
Gem'Hadar aren't that much stronger than strong humans. With Hirogen, it depends. If you go by how strong the writers say they are, Hirogen wins over Gem'Hadar. If you go by how they actually came off in the show, Gem'Hadar wins over Hirogen.
5 Gem'hadar vs Data, it really seems if Data is able to see them cloaked. If not they might be able to disable him with a surprise attack.