Valve, when are you gonna figure out that people just want more TF2, Portal, CS, L4D, HL, and maybe DoD? Like, I guess at least you've recently released a CS and HL game, but what about the others? TF2 seems like it's been on life support while Portal and DoD are completely forgotten.
I'm ok with how Valve is doing things right now. If they followed the same path of EA, Blizzard, and every other big developer from the 90s/00s we'd be on HL5, L4D9 Left for Deadest, TF 3 but it's a live service on season 15 and constant price increases on the season passes.
Let them experiment and dip their toes into new game types.
I'm sure there's some small game that technically invented it, but was rather obscure. TF2 was the first mass market hero game I can think of. I guess TF1, in some respects.
The "small" games that inspired, if not invented it were Doom and D&D. There was a Doom map called Fortress where you'd attack each other's base and the further you'd progress into your opponent's base, the better weapons it'd unlock for them to use.
A few guys in Australia combined the ideas in a Quake mod called Quake Team Fortress. Then they got hired at Valve to remake it on the Half Life engine as Team Fortress Classic.