While Overwatch and CS:GO are often games pointed to as the one that popularized and lead to the loot box/gambling popularly, TF2's implementation of crates/keys is a clear point of inspiration for those games :(

However I agree, the initial Free To Play decision wasn't a bad thing for TF2, though the culmination of that with the store/creator relationship and how things evolved in the company have lead to a less than desired development cycle for TF2 content when you look at what Valve actually provides in modern updates. And we waited how long for that comic? :P