well, the alternative is a rather risky partition switching back and forth between boot and recovery, enforcing of a kernel patch onto customers (to automatically force reboot to recovery on a panic to trigger the rollback there) and quite a set of code changes to snapd (there are a bunch of initial PRs for that already). the result will be a lot more porting work and code to maintain for potential customers, adding a 10sec reboot to an existing 30sec boot still levels that out IMHO.
how do you want to get more precise figures if you dont know how long the pre-boot bits take ? we can surely test on a dragonboard but that wont tell you anything about the future foobar-board that might have an SPL that takes 20sec on its own to initialize the board before switching to the actual second stage bootloader.
the figures we can measure are kernel and initrd and these wont be 30 additional seconds.
we also wont be able to do any measurements at all if we dont move on btw