In my case - clean boot takes 25s.

Clean boot yes. But I rarely start my workflow from the "blank" desktop background - there's prep and glam I like to do or tend to set up but that I would prefer to explicitly set up instead of it being done automatically / without my input, starting with the FDE unlock during bootup (defo not something that I intend to leave the system to solve by itself). It's one of the reasons why I like hibernate (more than suspend, anyway).

tl;dr: my workflow is not good for "true" powerdowns because it draws none to negative benefit from "clean boot"

All that said, wakeup from hibernate is snaily slow if one does not do some prep before hibernate and I avoid such interruptions where possible, but it's not bad to the point that clean shutdown → clean boot isn't worse.

btw. by default windows doesn’t do a full shutdown, but a sneaky hibernate

Huh... I suspected as such, as some Linuxes do also offer the option, but didn't expect that Windows would get hung up on the idea that someone else dared to take a look at the drive while Windows was not looking. Talk about yanderes. Thanks for the interesting info!