Sure, the original idea might've already been there, but they built the game all the same. Saying it "wasn't them" is misleading. They built it from scratch, with existing concepts from mods.
Maybe their ideas department isn't the greatest, but their execution on these games was very good in the long run. They popularized hats and make absurd amounts of money from it.
Let's not forget the Steam Deck. Early on still, but an excellent product in a whole different area.
Most of them have their origin in community mods, some already having gained substantial traction on their own.