Could you not just run Best Saber on a Quest?
It’s possible, but as noted in my other comment, the Quest version is notoriously unfriendly to modding and can chug with more complex custom maps due to weak hardware, which is problematic because I play modded/custom exclusively.
At home most gaming (including Beat Saber) is done on a nice custom tower that outguns any reasonably priced gaming laptop, meaning that if I bought a gaming laptop it’d only get used when traveling and would collect dust the rest of the time. Unless of course I sell the desktop and go laptop-exclusive for games, but that comes with some notable tradeoffs (fan noise and longevity primarily).
The Deck’s form factor makes it attractive for at-home use scenarios that a desktop and laptop don’t fit as well, and a such has a better chance of getting consistent usage compared to a laptop.