Ok, this will be a bit harsh, but…
1. If it’s time consuming to „adopt”, you somewhere lost your focus on the teams needs. Platform is not something to learn, platform is something which should simplify developers live. What I suggest is: select few teams which are slowly progressing with features delivery / are overloaded / request you the most of tickets. Choose one area and make it simpler for them (maybe it’s observability, or painful deployments? Or dependency management? Deliver them first simplification of their everyday sdlc)
2. There is a way to overcame it - make a company vide discussion on target technology stack. Involve COO / Enterprise Architects. Companies, even big ones, rarely really need diversity in tooling. Select the most teference teams and take responsibility for migrating them to the platform instances (but do not involve them much, because their focus should still be their usual business). In one company I just did enabling teams, both for migrations and for parts of the platform delivery - and invited developers from each team to join. Of course it reduces those teams capacity for a month, but then platform felt like it’s something they co-created, not something you forced them
3. metrics - I like those ones attached
Most of the dilemmas you are having I had as well. You can ash your boss to finance my course to make your live easier :) and I also do commercial consulting (first session can be free if you need help).
http://drogaarchitektait.pl/en/efficient-platform-manager-global/?trk=public_post_comment-text