This was my impression during the whole weekend. For me it seemed that McLaren was a bit more average, rather than Red Bull exceptional. (for sure the upgrades helped).
I think it is not unlikely that FIA found something in the grey-zone when inspecting McLaren's brakeduct.
It makes perfect sense to issue a statement that everything was legal in the system as they did not brake any rules. But at the same time they closed the loophole.
I take it with a pinch of salt for now, but it will be interesting to see some future hot races whether McLaren will stay superior under those circumstances before drawing final conclusions.