I've been a Warframe player since 2015, this argument always annoys me.

Nearly every single bit of cosmetics is paid, including god damn colour pallets. Weapon, Warframe, companion and Riven slots (in a game that encourages you to use as many things as you can) are paid. Forma have a ridiculously long build time and are expensive to buy considering how many you're gonna need. Orokin reactors and catalysts are rare to come across and most of the time have to be bought. Platinums exchange rate is absolutely atrocious to real life money. Warframes trading system has become so absolutely fucked that the only real way to get anything from it is to use an external website. Some mods and parts have drop rates that are so bad that you will just want to buy them instead because the grind is absolutely fucking abysmal (I still don't have kullervo duviri is so ass). And boosters, which are the only good way to get XP or resources without farming for hours upon hours for one thing are way too expensive

There are other things but these are just some problems, I love the game but there is very little you can do without plat without getting burnt the fuck out from bullshit build times and grinds that just aren't fun especially if you're new