It seems now that the flexi wing saga has subsided, McLaren's tyre temperature management is being framed as the next significant factor contributing to their main advantage. This could indeed be the case, and it probably is a contributing factor. However, I think it's not accurate to assume that rear tyre temperature management, specifically, is McLaren's biggest advantage over their competitors.
The discussion around their brake ducts, for instance, looks increasingly like a "smoke-show" rather than them being the fundamental reason for McLaren's perceived strong rear tyre temperature management.
Based on The Race report after the FIA's detailed inspection in Miami, they noted:
Formal confirmation of the McLaren all-clear comes after the FIA also clarified its stance that the use of any special tricks of technology to help cool the brakes or tyres would be illegal.
This put to bed any notion of the team using radical ideas like phase-changing materials to help better manage brake or tyre temperatures.
I also commented on this in the McLaren car thread previously. After thoroughly investigating the matter myself when the rumors started, it's clear that the Technical Regulations explicitly state that it is not permitted to use any medium other than air to cool the brakes. This significantly restricts the scope for exotic cooling solutions directly at the brake assembly.
In my opinion, this entire aspect of their performance is not a "one-trick-pony." The design of the rear brake drums alone cannot be the sole reason for superior temperature management, particularly from an area so heavily constrained by technical regulations. I think there's more to it and you would need to design the whole rear end of the car with it in consideration.
Finally, and perhaps most importantly, there's a tendency to entirely ignore McLaren's performance in Imola when discussing this topic.
You can't logically claim that McLaren's strong pace at Miami was primarily due to high track temperatures and then discard Imola as a relevant data point. McLaren was in a league of their own in Miami under those conditions. However, at Imola, where the race saw track temperatures ~ 3-4 degrees Celsius higher than in Miami, Max Verstappen was, at the very least, a match for them.
This brings up the question: which of these performances is the outlier? Because if you take both races into consideration, the correlation between high track temperatures and the performance gap from McLaren to the next follower significantly weakens. This suggests that while tyre management is a strength, its impact relative to overall car performance in varying conditions needs to be reconsidered.
The flexi-wing saga is not over yet IMO, we have to see maybe the next 2-3 races to confirm, however Barcelona is a good track to test its impact. Tough conditions on the race as well, but it seemingly did nothing to McLaren's pace in both long runs and low fuel performance runs.
But either way, I am mostly awaiting on RedBull's rumored rear corner updates. I am ready to eat my words if they make a clear jump in performance from that alone, but as things stand right now, I am personally very sceptical.