For PVP you can have Heart upgrades drop from wins. IMO losses shouldn’t bring in any reward.
For the rest - to be fair, I think WoW should more or less be designed as a complete package. Raiding, as the most challenging content should always give the best rewards. I think designing the game in a way where players can just ignore huge chunks of the game is wrong. For me, MMOs have always been like this - do dungeons to get the gear to be able to do raids. Do raids to obliterate everyone in pvp. Then you just have fun in pvp because it is competitive. Personally I don’t see the point in doing dungeons and progressing your gear if you aren’t going to use it in raids. M+ changes this, but not that much for me. I think at higher m+ keys, dungeons should change more dramatically - for example, have the entire map flipped horizontally, or have alternate bosses. So that for those who only want to do dungeons, there’s still some kind of “end” content that they need to overcome.