TF2 was their first major release that was free-to-play with purchasable cosmetic items, but their games have never been pay-to-win. They were historically pay-once-to-own, free to continue playing.
Firstly, stock weapons are typically the strongest among each class.
Secondly, you can get every item in the game without spending a dime via one of the following: 1) the drop system, 2) the crafting system, or 3) trading.
> Firstly, stock weapons are typically the strongest among each class.
While this is partially true, there's also a large set of items that are straight upgrades especially in competitive. The Cruisader's Crossbow, Ubersaw, Escape Plan and Gunboats are just a few examples of completely superior weapons and while their usage in casual isn't as wide spread you'd be hard pressed to find to find a serious competitive match where these aren't all being preferred.
There are also an assortment of weapons that are banned by competitive leagues because they practically break 6v6 gameplay. A good example is the wrangler + Rescue Ranger combo. With a good engineer it makes it practically impossible to kill a sentry.
I still agree with you that this doesn't make TF2 PTW for the other reasons you've listed, but it's occasionally been a problem in competitive when players don't have the "required" unlocks or the item servers are down.
I have about 250 hours in it, but I stopped playing in 2013. At the time, I found the drop system to be pretty unrewarding unless you paid for keys (or just bought what you want). Has it changed since then?