2011 is about when I started playing (although I have a copy from forever ago that I just never got around to, I have the "proof of purchase" in my inventory!) and yeah I'd definitely agree that f2p was the start of the "fortnite-ization" of tf2 where (what would become known as) casual play started to become the focus. I've heard it described as the "saturday morning cartoons of video games": just a silly little game, tune in next week for more fun. actually literally cartoons in the case of the bimonthly (rip) comics.
Before the proliferation of unlocks the game played a lot tighter as an actual game, let's say pre-2011/2012. 2011/2012 to 2015-ish is the saturday-morning cartoons period.
And I'm not saying either "serious game" or "silly little game" is better or worse, just that there's a bit of a tonal shift between, say, the pyro update and pyromania, right?
2015-2016 is maybe the tail of the cartoon period, that's pre-matchmaking, but also they started to have some bad ideas (iron bomber, parachute, air strike, nerfing combo pyro, etc) that made the game overall worse imo. Just a matter of taste but that's where they started circling the drain in design terms and going after some of the fun meme stuff, then later the e-sports thing came in and ruined it.
I think the irony is that the e-sports game they wanted in 2016 is already there, it's the game they had in 2011. But you can't take away people's unlocks and their hats, the things they'd pivoted to with casual made the pivot back to e-sports a lot more difficult, it's a lot harder to remove weapons from the game even if they don't fit what you're trying to make anymore. At best you can try for the "comp/casual" split (not that the split they ended up doing made any sense - 6v6 with no weapon/class limits? 12v12 with funhaving loadouts nerfed? that's the worst of both worlds) but the comp/casual split fractures the community too.
I think the other part of the problem is it's tragically unhip to have a 2007-vintage arena shooter as your e-sports title in 2016. I've heard the take "musk didn't want to own twitter, he wanted to own a network with twitter's size/reach that works and behaves completely different in every way". And tbh Valve didn't want TF2 to be an e-sports title, they wanted a title with TF2's userbase and reach that played completely differently from the thing they had spent the last 5 years turning it into. And then they took the CS:GO devs and tried to cut away the funny meme stuff and turn it back into a serious e-sports game and now it satisfies neither side.
But anyway yeah I completely get the feeling that TF2011 is a thing that a lot of people would like to play too, before things got too silly and too much about the hats/less about the actual game itself. I just also think that's really the serious e-sports game that Valve really wanted in 2015-2016 and they didn't know it.
Would love to see both TF2011 and TF2014. Hell TF2007/2008 would be funny too, let's have 6-pipe demoman and sentries you can't move (pyro kinda needs airblast though).
(actually the Xbox 360 version is frozen in time, because Valve refused to pay Microsoft to validate updates... it has the very first update because you get one free and welp guess that's it!)