I used Graphene OS on a Pixel 4 for a few years and loved it. I feel like I'm a total minority user who doesn't attach themselves to specific apps so not having Firefox available wasn't really a huge thing for me. There were several apps I did have to have, but they were all available through the F-Droid store.

Graphene was easy for me but like you pointed out, many will not use it because it doesn't have exactly what they use/need. To some degree this inflexibility reminds me of people not switching to the Windows Phone platform for the same reason - which is sad considering we only have two choices now because people wouldn't take the chance and Microsoft abandoned the OS before really giving it a good opportunity to thrive.

Kind of a sad state of affairs when people are totally comfortable handing over all their personal information to the likes of Apple, Samsung and Google.

Full disclosure: Yes, I'm a totally disgruntled former Windows phone user. Yes, there were a lot of factors that led to its demise, but I felt at the time we finally had an alternative to what we were being spoon fed in Apple and Google.