Ooh, this may be more worth a look then. I had hoped I'd be able to use the old phone to get up to speed before considering going to a custom ROM on my main device but it sounds like a Samsung S8 may be an exceptionally poor choice due to driver availability and other issues.
Graphene sounds like it addresses a lot of the needs that are pushing me away from stock Android (unnecessary bundled services, concern about Google harvesting more data than they should, Bixby / Google Assistant re-enabling itself every few updates and being pushed on users) but does so in a way won't sacrifice too much functionality (will definitely learn more about sandboxed Play services - that sounds useful).
I may have to consider getting a refurbished Pixel and setting it up with Graphene.
Actually, it still is relevant because custom ROMs often incorporate driver and security updates to the base ROM.
I know Graphene recommends against the out-of-support Pixels for this reason.