The beginning of the end was the loss of Gullett to the Yankees due to free agency.
Fresh off the 1976 title the free agent draft started, rather than pick players like most of the league the Reds decide to address their picks with a single statement and a stance that would hamstring the team in the early eighties as they faced a rebuild. the statement was this:
“In fairness to the players who have won the World Championship for us two years in a row and considering how our organization is structured. We do not think it would right for the Cincinnati organization to get into the bidding contests that must come out of this draft.”
Add the fact that Howsam hated Perez's agent (who also was Eastwicks) and you can see how resistance to the new economic structure slowed the team down, if they had played the market correctly they could have patched up holes with FA's and maybe won 2 more titles in the 70's.