I believe you're missing the actual causality chain here.
While it is actually proven that vendors will degrade your experience artificially to "motivate" you to buy new devices, in the never ending pursuit of monetary gain, there is no such potential incentive here: you aren't paying for new drivers.
And while others suggest biases, I do believe you are witnessing an effect that is at least partially real, if not totally, but not for the reasons you believe:
Most programs that leverage GPUs end up being GPU bottlenecked. Meaning that one can almost always improve the program's performance by using a better GPU.
But then, why does a new driver not improve performance, and rather, simply "bring a degraded performance back to previous levels"?
Well, that has to do with auto-updates, and the way drivers are distributed.
While, in a world where one would have to manually update everything, a new driver would almost certainly mean better performance for a given program, most programs in our world auto-update automatically (and sometimes even, silently). And the developers are usually on top of things wrt drivers, because they follow drivers updates closely, get early versions, etc.
Meaning that when a driver is updated, your apps usually are, too. In a way that leverage the new driver for more processing, rather than faster processing. But unlike your automatically updated apps, your drivers are updated manually.
And the consequence of such updates, when you are too slow to update your drivers, is a degraded experience.
Not because anyone artificially throttled your device's performance, but because you lag too much behind expected updates.