TDP is about as meaningful on CPUs now as nm is in fab tech.
In practice the 3950x pulled up to ~225w running maxxed out avx2 workloads, ~300w if you overclocked it. The 3900x pulls up to ~190 watts at stock boosts. Both are called "105w TDP" parts.
This is incorrect, to the best of my knowledge. 3900X and 3950X both have a 142W package power limit (PPT, 35% above TDP) at stock, with a properly working motherboard. As I understand it, not even short boosts are allowed to use more power than the PPT.
The limit can be lifted in the BIOS (or e.g. Ryzen Master) but that would no longer be stock operation. And there was a defect in the initial BIOS of ASRock X570 and maybe other motherboards, which broke PPT but that was running the CPU out of spec, not stock operation.
If you're going to attack the "spec" that is TDP, you may as well do it correctly. None of the scenarios you mentioned align with what TDP is supposed to "measure". Even if TDP weren't the flawed measure it is, you still wouldn't be critiquing it by noting the measures you have.
I disagree. If TDP wasn't so flawed as to be completely meaningless, that critique would probably be valid.
The definition AMD uses is absolute nonsense, given how much the θca values differ from model to model. If they fudged any harder the higher end CPUs would start having "TDP" lower than the weak CPUs.
In practice the 3950x pulled up to ~225w running maxxed out avx2 workloads, ~300w if you overclocked it. The 3900x pulls up to ~190 watts at stock boosts. Both are called "105w TDP" parts.