Also needs mentioning: clustering. I have a years old cluster with none of the hardware I originally started with, but my Pi-hole is still there. Having the ability to migrate guests between hosts is a game changer when you frequently replace or rebuild said hosts. With the right setup, migration can have as little as a few seconds of downtime, or even no downtime at all. You can’t do that with bare metal installs.
Agreed. I would also reconsider ditching the ISP router. You can still connect your gateway to it, and having the ISP device on premises can mean they might not blame your equipment for a line issue.