My P1 isn't great either, largely due to the nvidia GPU consuming more power than anything else in the machine. But other lenovo laptops (with integrated GPUs, and AMD cpus) are pretty fantastic on the battery lifetime front.
That said, I think the software stack these days has more to do with it than anything. As I mentioned in another comment its entirely possible to get the power consumption of AMD laptops into the 3-4W range with a modern linux kernel, light browsing, emacs, etc. And that is largely in my case due to assuring there aren't any background tasks consuming CPU time, and running powertop --autotune, assuring inactive HW is turned off when its not being used, cpus are spending most of their time in deep sleep, etc. All stuff that the mac is basically doing out of the box (or running background tasks on low power, etc cores). While I'm getting 15+ hours out of a fairly pedestrian 65Wh battery, which is pretty amazing since the screen and assorted devices (disk, ram, etc) are probably 1-2W of the total. Now all this goes to sh*t when I start running a compiler, or other CPU intensive work, but from my experience that happens on the M1 macs as well, which can get quite toasty and kill the battery life if left building software for an hour or more. Powertop, turbostat, cpupower are all useful diagnostic tools as well as disabling stuff in the BIOS, or powering stuff off (or at least into lower power modes) via the kernel/ACPI power methods.
(presumably some of the more efficient intel might be good too if one clamps the CPU freq/etc I've just not tried one, but i'm pretty happy with a couple of their older generation i3/i5 desktop machines).
Windows used to be reasonably good, but I get the feeling the new generation (modern standby anyone?) isn't as dedicated, and hence the machine isn't forced into a S3 like mode when the lid is closed. Combined with the apparently fragmented way the OS is built means the people in charge of power mgmt can't tell the people in charge of windows defender to get bent or any other part of the platform that excessively consumes power. So that said, the P1's support linux, which means there is an option for S3 in the BIOS, flip it on, and run the windows task schduler/runon/etc features and kill anything that can wake the laptop. That should keep it from running the fans in your bag. There used to be an option in the windows power control panel to select the action for lid close too, if its still there, then set it to sleep (S3) or hibernate (S4).