I think it isn't about amount of hours you spend, more like the hours you spend developing.
Look at this way, we all grow up in a society where we speak the native language, but we don't advance our language skills without the right resources. I developed my vocabulary to a certain level in School/College doing English Literature, reading multiple books and examples of great literature and word play. Granted over the years my career has shifted to utilising these skills less and less, so as a result I have had to use the spellchecker no less fewer than four times, though it is mostly your Americanized use of the 'Z'. But as I attempt to learn German, I notice I can consistently do the easy/basic stuff but then it takes a lot of practice to move to more intermediate and advanced levels of the language, something I have to consistently do. So I can keep practicing basic German phrases and sentences like "I have a dog" all day long, but then if I want to expand on it I need to step my practice up and do more advanced types of learning.
How does this relate to TF2? Well, I have just gone over 10k hours, I estimate 95% of that time was actually me playing so I think I can say I fit into the discussion well. Of this time, I don't think I played competitive TF2 until after I had played at least 2000-3000 hours of the game (Can't remember) but I spent most of my gaming time, several hours a day sometimes on cp_lazytown or Goldrush or Dustbowl or other choke point spectaculars playing Demoman and Engineer, camping with a sentry and being the master of sitting back on my last or alternatively as Demo, spamming choke points waiting for the inevitable 12 fov pub player to run into my spam and die.
So after 2000-3000 hours I try pugging vs what is by todays standard, bottom feeding Div 6/Open/TF2center level players and get rinsed upon. All my experience spamming a choke point tinier than the Oesophagus of an ant and camping on a point with a sentry meant nothing when scouts could press A and D once or twice and wow my puny public player game. When you compare this to the majority of competitive players who sit aroun 2k-3k hours mark, some of them are quite good but that is because they spent the majority of their practise time learning TF2 in a more advanced competitive environment, on bigger maps which require more advanced skills, versus better players and of course utilising the cookie cutter setup, so you can try appreciate the disadvantages of certain classes in a higher stake, higher skill matchup. I spent most of my early hours not learning much, just repeating the same basic and easy skills it to be successful on certain classes. It was only when I started spending the next few thousand hours practicing in more advanced settings (and learning about the game) did I start to see improvement that enabled me to play a higher level.
Once in a blue moon I revisit Lazytown where I started to game and see some of the same faces there, their TF2 hours starting to jump into the 5k+ region and still, still they run in straight lines into sentry guns as Pyro. It isn't the amount of practice you do, it's the quality of practice.