Lets just say that i7-9750h is a thermal throttling behemoth, half of the threads in here someone has one of these things throttling. Looking at the specs of ryzen 7 3750h (never seen one myself) and thermal design of these laptops (unless its very thick model which is a plus) you will end up thermal throttling hard whatever you choose. Thing is with intel you can undervolt easily but idk if ryzen allows this, someone can comment on it i have absolutely no idea, never undervolted ryzen laptop.
If youre willing to repaste with thermal grizzly kryonaut and undervolt, use a cooling pad etc i would still go with i7-9750h it has stable performance if do atleast 2 out of 3 of these things i mentioned.
Dont think too much for my recommendation since i never had ryzen cpu laptop or ryzen desktop. Only thing i can say that look for thermal benchmarks, pick the LOWEST temperatures you can see under load whatever manufactor you pick. Theres no point in looking benchmarks on these cpus if your gonna downclock cause of overheating, this will also affect GPU clocks depending on how manufactor wanted the thermal design