I'm not sure I've ever played an MMO where you couldn't purchase an advantage or PtW .. The definition of free to play has changed over the years. Depending on how you define it, Wurm Online is F2P.
Path of Exile is a great game, however ... VERY early on into gameplay Path of Exile players will find out they're hindered by their lack of "bank" space, and must pay real currency in order to have larger storage. It may not seem like it at first, but it certainly is an advantage as hoarding good items/currencies to sell in the game is one of the fastest ways to progress in end-game. Imagine playing Wurm with nothing but a large cart and needing to pay for more space .. no type of item is "too large" for the default banking space in Path of Exile compared to a large cart, but you get the idea.
Warframe is also a great game, but you can buy the majority of rare crafting materials off the platinum (in-game premium currency) store. Advantage. Not to mention the trading of platinum for end-game blueprints you'd typically have to grind for. Platinum = WO silver. Most (as I can't speak for all) of the other games on the Steam F2P list have some sort of premium or pay for an advantage option. Albion, Crossout, War Thunder, World of Warships, etc, ALL have premium or premium-like services for paying players. Googling "Free to play MMO" doesn't help too much either. I've never played Neverwinter or StarTrek Online, but everything from TERA, to Runescape, to EVE Online ALL have premium or pay-for-advantage services.
As far as I know there are two major ways to monetize an MMO; 1) Buying outright with no in-game monetization .. Guild Wars 1 was a good example, but even Guild Wars 2 and World of Warcraft (not classic.. yet?) have headed toward a pay-for-advantage direction. 2) F2P with in-game monetization aka paying for an advantage.
… and of course many games have a hybridization of the two types such as Black Desert.
Just my 0.02
Edit: I also want to add that I think games in general are pretty fairly priced. I'll continue paying for these products because I enjoy them. Only meant to share my experiences with these other games to quell any potential for misinformation!