It's not really my logic, it's how the FIA have enforced this over the last few seasons - they did the same with Red Bull's wings. They do make mid-season changes in some cases, although only when things are particularly egregious. And, honestly, I think the more consensual, measured, approach of the FIA recently has been a good thing. I'd rather the teams had some certainty about how rules will be enforced, and where things are grey they're given a chance to change the parts rather than getting disqualified. Post-race disqualifications can be justified, but if it can be minimised without compromising things too much? Well, I'm in favour.
I'm not convinced the wing makes that much difference, and while McLaren won this race, I think the Ferrari was faster, and Pérez showed the Red Bull was capable on winning a podium, possibly even the race.