I don't know about the Byrds, but the Monkees weren't even musicians. (Well, one of them was.) They eventually did learn how to play. I bought their "authentic" CD, "Headquarters", and it is, to put it mildly, devoid of any interesting music.

The best thing that ever happened to the Monkees was to have Hollywood write and perform the songs for them, while they lipsynced, clowned around and looked good. The best songwriters in the business wrote their songs. How lucky could they get?

The Monkees were not ripped off in any way. The value they received was becoming famous, and that has enormous value they can use to make money off of anytime they please (and they have done so).