I thought the Nuggets had two strong teams / eras.
So the late 70s with David Thompson. Then his drug issues and decline ruined the team. Along with the trade of Bobby Jones to McGinnis who had one good year before that fell apart as well. So they ended up losing 2 of their top 3 players in quick successio. That team was one of the better teams in the league during that 1977-79 period or whatever it was exactly. Around then.
Then they had a lousy period with Kiki Vanderweghe. Those Nuggets teams were never up to much. Middle of the pack squads. Slightly below or slightly above middle but middle always. They never had enough defense to compete with the better teams in the league (god awful defensive teams). This period ran from 1980-84 roughly.
Then came the breakthrough trade of sending Kiki to Portland which not only netted them a quality replacement who better fit alongside A English in Calvin Natt but also brought on board to other important players who would rejuvante the team. Fat Lever who was drafted in this and has been talked about. And Wayne Cooper who was the best interior defender & shot blocker they had had up until this time and would be throughout the remainder of the 80s.
These two (Fat Lever & Wayne Cooper) combined with TR Dunn (defensive SG) and Bill Hanzlik (defense wing) gave them 4 strong defensive players to put alongside their offensive talent - holdovers A English and D Issel along with two-way player & newcomer Calvin Natt. They would be the foundation that would lead to another strong Nuggets team with postseason dreams.
These dreams wouldn't last long. Issel was on his last legs. He would retire soon after. Maybe 1-2 seasons. I can't remember. Then Calvin Natt started to decline. They only got 2 years out of him. So 2 of their top 3 scorers were out of commission (again!). This is when Denver got in trouble again.
I was listening to an interview with A English and he said they never managed to reload again after that. That they made several draft picks which failed to pan out. That management wasn't able to find any way to refresh the team with new talent. Essentially, not enough top tier talent outside of A English and F Lever for the remainder of the 80s. So no more title hopes.
In that interview, English also praised the Kiki traded for turning things around for them because it was a "3 for 1" trade. They had 3 quality pros in exchange for 1. C Natt, F Lever, W Cooper. That is what lifted them back into contention in the West.
So they had this bright team for 3 years or so in the late 70s and only 1-2 strong seasons in the mid 80s. The early 80s were a mess. And the late 80s did not have enough high end talent. So out of that 15 year period they had maybe 4-5 years of postseason hopes. The rest of the time they were never in it.