The original era of J&D is all that matters, from a relevance standpoint. J&D never had hit records again, either together or separately. The re-recordings hurt rather than helped, as they flooded the market with false advertising, and did little to steer casual fans to the original recordings.
The bottom line is that Jan had three lucrative (creative) contracts with Screen Gems, and was highly paid during J&D's original era. Dean was not highly paid in the original era. He did okay (far better than many), but nothing approaching Jan's financial situation. Those contracts gave Jan deadlines to meet, with consequences if he didn't.
You'll see the breakdown in the Sessionography. I'm very close to having 1964 ready for publication.
After the accident, Jan was never himself again; and Dean is right. Jan was always frustrtated.
The oldies touring act gave Dean a chance to finally make the most money between the two; and Jan got to be on-stage. And fans got to see them together. Live performances were never Jan's first love, but they were all he had left on a consistent basis (aside from his occasional studio sessions and releases). At least Jan did continue to write, record, and release new material on occasion.
And in the final analysis, they each needed the other to make it work -- in both eras.
Dean's own sister summed it up pretty well in 1977:
"He didn't get that much involved in music. I mean Jan was the one who really got involved with the producing. Also, Jan was a lot stronger character than my brother was . . . like cool . . . and the girls fell over him. My brother was one of those who kinda watched it all . . . stood on the sidelines, you know. He was always kinda there . . . right place at the right time, but he wasn't the one who was putting in all the big energy. He kinda went along with it all. He lived with my mom and dad for a real long time. Like when he was 19 up to when he was 25 he still lived at home. Jan (on the other hand) had a house . . . whereas Dean liked living at home and saving his money, and having a nice Corvette. His parents and me kinda bolstered all the insanity away from his life. He didn't get into drugs or hang out with weird people."