AMD's recommendations are just that, recommendations. You can use whatever you want. But when reputable review sites such as Techspot and TomsHardware show that even powerful closed loop coolers AT STOCK (no PBO) are struggling to keep the chip under 75*C in real world usage, the fact that Turbo frequencies are heavily dependent upon temperature, and the fact AMD doesn't list a thermal maximum (as of this post time) on the specifications page so you don't know, officially, what the maximum operating temperature is, if you want to risk your $750 chip on an air cooler, even though it may be listed as compatible by the manufacturer, feel free to, but AMD doesn't honor any warranty when the chip has overheated, and retailers don't accept any returns for lower than expected performance.
https://www.noctua.at/en/nh-d15-se-am4/?tab=cpucomp
This article mentions that Air can be as effective as Liquid but Liquid is more efficient at removing heat:
https://www.gamingscan.com/liquid-vs-air-cpu-cooler/
3rd generation processors are much more different than 2nd generation processors and earlier. They heat up differently due to the way the chips are aligned inside the processor case.
See this previous AMD Thread about a User using a Noctua Air Cooler having high temps on a 3rd generation processor: https://community.amd.com/thread/244048 . Some of the Users explains the difference in the 3rd generation processors in how they heat up.
In your case, I would follow AMD recommendation in getting a Liquid cooler since they are more efficient at removing heat than air. Actually this is the first time that I see that AMD recommends solely liquid CPU Coolers for one of its processors.
black_zion, AMD did not initially list a Max Temps for Gen 3 processors. Ryzen Master always listed it and AMD started including it in their specifications. For some reason, the current 3950X specification does not have a Max Temps. Here is the specification for the 3900X. Enjoy, John.
Remember the 2700 and 2700X though of the previous generation, the 2700X had a thermal max 10*C lower than the 2700, so it is possible the same thing could apply here, the 3950X may have a Tmax of 85*C as opposed to the 3900X's 95*C. As far as TDP goes, AMD "lies" as much as Intel did with the 9900k, they're both 145w processors at stock (no PBO).
