To start that's why I said to stop calling them untradeable and just make them unsellable, meaning no coins, also I've got tonnes of untradeables that aren't better aswell though? If untradeable players are better why have I got so many 80 rated rare golds and the like that are untradeable from my rewards? Surely if the untradeable cards are suppose to be better then rewards should be better no?
Let's just examine squad battles. With the rewards I get I'm likely to get around 21 players with only 3 guaranteed to be better than an 86, whilst they may be tradeable the probability of me getting anything worth selling is probably like 10% at most. The future stars are untradeable, but I'm likely to just get the same shoddy 87 rated players. Just say that in 3 days time I need some players to do a team of the week upgrade for an 83+ x 10, I would much rather trade one to someone who may need a higher rated player for a few 84 rated players, rather than waste my slightly higher rated players.
It's not abusive, it's not cheating, it is just simply a way for players to make more use of the pile of cards that they don't actually want, and probably never wanted or needed in the first place. That is why I don't see the issue with creating a swap market, especially if you put everything in place to make sure it is extremely hard to abuse.