But the regions include Sett and Samira? So I can just farm them? That's what I really want to know
You can farm any card in the game. There are free players that earn cards faster than they come out; people with 100% collections of every card in the game that have never spent money. This takes months to years of free play to get 3 copies of everything of course, but that's literally *everything*.
If you are thinking of spending money and want to get a specific card and don't have green shards or champion wild cards yet though, you can get a coin bundle to buy them directly. If you want to be hyper-efficient, the event pass has lots of cards from the just-released set on it in its chests (plus other cool stuff).
If you prefer PvE or Roguelite experiences, The Path of Champions mode also offers a way to play with Sett or Samira (samira unlocks for free on the current event pass, Sett unlocks for the premium version of the pass).