It's not really a question of whether you like it or not though - it's a question of getting improvements, even if they are marginal, to get back into the top four. Your concern would make sense if signing Leno would consolidate our place as a Europa league team.
I have no opinion of Leno, I remember him being highly rated and he's clearly stagnated but at 26 he could re-invent himself again. Who knows? Predicting how goalkeepers turn out is possibly the hardest thing to do in football. See: Szczesny, Lehmann, Navas etc.