Fascinating discussion...as an American who's now watching Swansea because of Morris and Arriola, the concern about the owners forcing this player on Cooper is interesting. I can't speak to this, but I will say that most American fans would say that Arriola's level is probably mid to upper championship--he's an above average MLS player, but he's nowhere near best 11 or anything. I don't know enough about your right wingback to say that Arriola will challenge him for playing time, but he works his butt off and puts in a shift, he's more skilled than a lot of guys who are playing the position at championship level, and at the very worst he's going to be a great depth piece for you. His floor is pretty high.
As for Morris, his ceiling is much higher but his willingness to fight for his spot (he hasn't had to in Seattle) is less known. From an American perspective this is great business for you--he gives you another striker for a busy calendar, and he's a guy that MIGHT end up being very very good in the Championship. Not as much of a sure thing as Arriola, but potentially also much much better. Don't know Cooper beyond the fact that he hates subs (right?), but both seem like some good business for a run at promotion and I can't imagine that he doesn't see it....