He had some of his best years after the Okie State thing, although he never won another regular season league title. I think the 1980 team that lost to national champion Louisville in the tournament was his best and could have gone all the away. Team basically had the Big 8 wrapped up with road victories at Missouri and Lawrence before it was struck by injuries. Got healthy and won the post season tourney but ended up with low enough seed they had to play Louisville early.
The decline wasn't so much about recruiting but failing to keep young players on the team. rough ridin' combover Purdue coach and his squeaky assistant stole point guard Reed (Reid?) who went on to become two-time Big 10 player of the year (maybe it would have helped had Hartman played him a little bit during, especially with the injuries) and two 6-8ish forwards, who went on to have fine careers at like MAC schools.
That meant he had to rebuild when Tubbs, Norm Stewart were in their prime and Larry Brown arrived in Lawrence. Then he started having heart trouble. I think he began to believe he could spot DITR and win, after all he had done it dating back to Walt Frazier. But without a superstar like Evans or Blackman, the guys he brought in couldn't get it done.