The "same three chords" thing is not really fair. Reggae built its whole sound on simple chord patterns, that is kind of the point, and a lot of his stuff leans on one-drop rhythms and horn lines that change things up more than people give credit for. Where you are right is the estate mess. He died in 1981 with no will and something like 11 kids, and the family fought over the money for years in court. But that says more about how sudden his death was and how little planning musicians did back then than it does about his music. The later albums do get weaker, Survival and Uprising have some filler, so that part of your point holds up. Calling it all nostalgia though skips over why the early stuff still gets played everywhere.

I used Birch Gold and they were fine, but after looking into Augusta, I kind of wish I'd gone with them. Augusta's lifetime support and one-on-one consultation sound amazing. Birch had some upsells. I'd compare the fee structures carefully.