The trick is, like you say, to do both.
But your second point is baffling.
A domestic cup gets you Europe. It gets you a title. The aim of football is to win things, not finish 5th in the league.
Obviously our league form is a major let down and the reason we're underachieving, but ultimately a cup is always better, IMO, for a side like ours that hasn't cost £500mil etc etc.
I was two months old when we last won a trophy. I've never actually 'seen' us win one. I'm sure winning a trophy would mean more to our players - especially the young ones - than finishing 5th would either.