I'll throw in as a factor here that I just barely have seen P Bradford (1970 doesn't count) and have seen a bit of Dirk toward the end, and all of Tate, but not the other RD characters mentioned, or as a kid only, and I don't remember them.
I'm not sure Dirk or Tate could have been anything more than they were, as played by RD. Not complicated characters. They were at their best when worked up.