Anderlecht also won the Uefa cup and they won the belgian championship 3 times in the 70's and 4 times in the 80's, far from a walkover.. and there wasn't much gap beetween the top european leagues and the others compared to today.. Dynamo Dresden reach a Uefa cup semifinal in 1989 and before them, Leipzig reached that stage in 1973..Magdeburg won a CWC and finally no East Germany team ever reached a EC semifinal
The Belgian teams who won in the other years must have been very good teams as well then. I'm not saying the UEFA Cup was some sort of really difficult to win competition like the Champions League is today, just that it was tougher than the European Cup. The average route to a UEFA Cup final was much tougher than the average route to the European Cup final. It just so happened that Dresden got a pretty easy draw in the UEFA Cup that year compared to some of the other teams (seriously, I had a look). They were regular quarter finalists in the European Cup, but they were likely to run into one of the big German, Spanish, Italian or English clubs at that stage.