Our model previously (with the likes of Mane, VVD, Wanyama) was buying the better players in smaller leagues who we hoped would get better, obviously they ended up leaving to the bigger teams. More recently we have signed players who have been at bigger clubs and, for whatever reason, wanted to move on (Lemina, Hojbjerg, Bertrand, Gabbiadini, Ings, Carrillo). These players might not be in such a rush to move back to a top club due to previous experiences there, or the bigger clubs might not be in such a rush to sign them as they may not have been deemed good enough which is why we signed them in the first place.
I am perfectly happy if we sign a player and he does well enough for us that the top teams come sniffing, means we/they most likely have done well in their time here. If they want to kick up a fuss about moving on after a year or 2 then fine, that is just football. We absolutely should be trying to sign the better players from smaller leagues that the big teams don't need to take a punt on. Hopefully Elyounoussi will fall into this category.