It's not recent. In late 2021, many apps didn't even support 120 Hz yet. The cap was definitely implemented in macOS Monterey, just might not be on the first release.
I do remember checking this initially up until around mid 2022 during some trips where I didn't have regular access to outlets, and I'm pretty sure the entire ProMotion option is just gone when Low Power Mode is toggled, leaving only refresh rate options in the System Settings page.
Granted, I have not checked it at all for the past year and doing it now does indeed keep "ProMotion" around. They also completely redesigned the System Settings app with Ventura, so maybe they did also fix a few long-standing bugs with the UI in Monterey. There were a few more odd ones related to the Display page and how HDR can be enabled/disabled.
Still, MacBook is not the same as iPhone. Apps and games not made with Apple's specific UI frameworks will still kick refresh rate to max. For instance, here's Shenzhen I/O, which is static and can work just fine at 24Hz but doesn't.
In this case, playing this game on the Pro 14" without any limit to ProMotion can cause massively higher power draw than the fixed 60Hz display on Air 15". Sure, you'll say... this is probably just because of the game. But it isn't even the only case where this happens. Here's more:
Why would a blank white page need to stay at 80fps and kick the display up to 120Hz?
So yes, ProMotion may help with battery life on iPhone, but not really on MacBook. At least not because of the max 120Hz option. There are plenty of examples of apps and games that cause massively higher power draw for no reason while ProMotion is running. These apps and games are not as uncommon as you think.
P.S.: also there's currently no way to "Limit Frame Rate" on MacOS as far as I can tell with ProMotion on MacBook like there is on iPhone. Not without engaging Low Power Mode. So if battery life is needed but no compromise elsewhere, setting the display to fixed 60Hz is still the only way that I can see.