There's a reason for that, macOS loads a specific fan curve that prefers silence over performance, only kicking in a the last moment before the CPU overheats. This focus on silence also costs them in performance, but as long as the laptop is fast enough for most people, the raw performance probably doesn't matter to them.
Windows doesn't about the thermal limits Apple put into place in their devices, so just treats it like a regular old laptop: boosting with fans turning whenever it needs to. However, it needs drivers to read the temperatures from the device and as far as I know, the Windows driver for reading those on Apple hardware aren't great (if they're available at all). This means Windows on a Mackintosh will always perform worse, because it doesn't have the same thermal information input as macOS has.
This sounds completely made up.
If you have more info than pure conjecture, please share.
I would wager the sensor drivers for Windows were written by apple.
"If it chooses to, Apple could resolve or mitigate the issue with a firmware update that kicks in the fans sooner"
Stuff like this is why I keep saying that Apple is a fashion company, not a tech company. Or more accurately, they're a company that makes technology fashionable.
But apparently fan noise isn't fashionable, so they try to eliminate it, even if it comes at the cost of performance in what is supposed to be a performance-oriented configuration.
Windows doesn't about the thermal limits Apple put into place in their devices, so just treats it like a regular old laptop: boosting with fans turning whenever it needs to. However, it needs drivers to read the temperatures from the device and as far as I know, the Windows driver for reading those on Apple hardware aren't great (if they're available at all). This means Windows on a Mackintosh will always perform worse, because it doesn't have the same thermal information input as macOS has.