I'm glad you're enjoying Adobe Lightroom. Before switching to Pixelmator Pro on my Mac, I used Lightroom, and it was phenomenal yet a tad complicated for my taste.
Regarding Apple Photos, I believe it is underrated because, for most people's needs, it is more than enough. If you look at the user persona of Mac users who primarily use their devices for content creation, the majority probably don't have the capacity to learn Lightroom as most Adobe products have a steep learning curve.
I agree that in terms of User Experience for Pro users, Adobe Lightroom is miles better than Apple Photos, but the primary function of Lightroom is photo editing, whereas Apple Photos is a photo manager with some editing features.
I wish Apple would drastically improve the image adjustment features of Apple Photos as the User Interface is not on par with the gallery view and memory features.
I want to Thank you for writing your opinion. This means a lot to me, and I learned a lot reading about your frustrations with this app.
Let me know if you'd like me to write more stories like this.