To your point, Warframe is a full game with a F2P model that only offers cosmetics and in-game currency for purchase, the latter of which you can earn through grinding and selling items in the in-game market. It uses the aforementioned "wait times," but they're not overly lengthy, given the amount of things you can do while you wait.

So with some extra effort, you can get the paid experience, but you don't miss out on any of the actual game by skipping that part of the grind either. Plus, in the end, even paid players can't defeat the RNG gods.