There's basically 4 ways they could make you get mons in Champions:
Home transfers
Premade rental mons
Download other players teams via teamcode
Showdownesque teambuilder
Transfers have to be one option, but they also can't be the only option if phones are a way to play the game that doesn't require a console purchase. Rentals tbh seem like a lot of busywork for GF(1000 mons, multiple formats, maybe unlockable sets, etc), but they're not impossible. "Use other players' teams via code" seems fairly likely, they've done that a lot in the modern era. I can't personally see GF ever implementing a pure teambuilder, it just goes so counter to their philosophy in various ways, even if it's obviously good for the format.
Now, what will Champions have as playable content:
Official VGC tournaments. This is confirmed. It also guarantees sales of about 10 copies if it's the only thing Champions does. Competitive playerbases are, almost by definition, tiny.
Battle sim for all other official formats. Definitely happening. How much that sells is a question, certainly it's only a small fraction of the mainline game purchases that ever play a single multiplayer battle.
A battle tower/Pokemon Stadium setup. (fair battles, diverse rulesets, player vs AI). This is interesting. Post-game facilities are loved by a vocal section of the fanbase, but it's a small fraction. Meanwhile, the Stadium games sold reasonably well depending on your point of comparison. (My personal theory is that the Stadium games being easier, to the point of in-game teams being viable, was crucial to their success). However, setting up 4-8 battle facilities/rulesets/associated NPCs is a lot of work. If it's a game sold for cash, I think they include this. Maybe with only a couple facilities early on and then free DLC of new ones whenever they need a burst of hype. If the game is FTP, no way.