tho you could argue it's not moral or fair to these teams

There is nothing to argue about lmao. Taking a club's main goalscorer after the transfer window closes is going to fuck up their season so even if it's legal..it's a dick move because it maybe easy for big clubs like Barca to find quick replacements and pay for them but that's not the case with the small clubs.

but you have to get to an agreement with the club or pay the clause

Yes, you'll pay the clause and get the player. Not to mention there is always a chance that Barca gets a player they want to act like an unberable cunt so there's that.

I don't think that should qualify as classless

Lol ofcourse you don't..it's normal for you.