Most problems with cooling aren't because of air flow. You can't cheat basic physics so if you use air to cool something down, you need certain volume and flow rates. Does your console still work? So it's properly cooled. Is it a whiny bitch like my PS4Pro? The fan is operating at higher speed so it doesn't overheat (because then it shuts down to protect it from frying).
Most problems with cooling happen on the contact between the chip and the radiator. If it doesn't stick very, very tightly, you'll get air between them. Air is a good insulator (so it's bad in this case). To prevent that situation, thermal paste is used. But it may be badly applied (imagine some poor Chinese guy assembling his 50th console that day),, or it may wear over time. Another thing is dust and other particles inside the box and fan wear. I'm not sure if PS fans (I don't mean ponies here

are stock pieces you can buy easily.
Anyway, I need to open my PS4 soon before hot days come, clean it, change the paste, maybe polish the radiator surface, check if the fan can be replaced... I don't recommend doing that on your own if you have no experience.
I agree with your point about air insulating, and the need for “contact between the chip and the radiator”, however, in my experience CPUs have a huge thermal window to operate in; a mobile Core i5 in a laptop being passively cooled because of broken fan can handle 70c for an hour before shutting off to protect the chip from my experience. IMHO I don’t think a whiny Pro is the result of an overheating APU – unless getting the PS4 OS official overheating message that probably indicates a fan fault.
I’m pretty sure the console memory temperature is the main culprit for whiny fans. The memory industry sees performance increases linearly, and processor industry sees performance increases at a quadratically rate. So I suspect console engineers have less latitude to improve memory bandwidth significantly without pushing too close to the limit. As an example, in the original PS3 repairs failing to return one thermal pad to a memory chip (or even a tear in one) would result in a failed repair. But in the first instance I’m not suggesting you open your Pro at all to replace thermal pads, clean fans or use new thermal grease, primarily because of a situation with my friend’s whiny Pro I fixed.
So my friend’s Pro had been running quite loud for awhile, but he assumed it was fine other than he had annoyingly lost use of ATMOS in his 4k hdr setup and could only get Dolby surround, and his 500GB was always full requiring him to delete a game before getting a new one. After getting him to replace the 10m hdmi lead with a better rigid cable – as I assumed the loss of ATMOS was hdmi handshaking errors - his ATMOS sound returned, but the console was then running so load it sounded like it was going to take off and every hour or so gaming he would lose picture for a few seconds. I was going to service his Pro for him with new thermal pads, dust with compressed air and thermal grease the APU when I got the stuff, but in the meantime he got another friend to crack it open and dust it out the fan, and it made zero difference and the console was as loud as ever. So when I saw him next, we took the fan access panel off, had a look and I vacuum-ed the side vents too using a paper straw as a vacuum mini funnel, which again made no difference...remembering his HDD was always full, I suggested the drive could be on its way out – something that would massively stress the console’s memory, so as a first check, backuped up his saves to the cloud with PSN, removed the PS4 hdd, formatted on a PC with a full format – had to cancel after 120GB it was going to take a day and a half – then did a quick format. Downloaded the full sized PS4 firmware from Playstation, and then inserted the hdd in the ps4, and restored the PS4 firmware and his saves from PSN, and his consoles is now quieter than before, but with ATMOS working, so well worth a try before breaking Pro security seals IMHO..
Obviously, not much of this is relevant to the thread, other than how it applies to issues that both XsX and PS5 will face with noise levels and thermals, along with choices about memory. And the benefits off going twin GPU if it allows for running two memory pools lower, while effectively adding their bandwidths without the same heat and stress of a single pool at twice the bandwidth.
If the DDR4 memory rumour for PS5 is correct then I would expect the DDR4 to be situated between the GDDR6 and Sony using heatsinks to let GDDR6 dissipate excess heat through the DDR4 modules.