Klopp won Bundesliga with Dortmund twice against Bayern and led them to a UCL final destroying Mourinho's Real Madrid 4-1 in the process (I know, Real was their nemesis at Liverpool). SAF faced Real three times with United, and got eliminated all three times.
Those European Cup you're talking about, teams like Dinamo Tbilisi, Carl Zeiss Jena, Standard Liege, Rapid Wien, Fortuna Dusseldorf, Austria Wien, Goteborg, Dundee United, Videoton etc. were playing finals during that period. That's not to say Aberdeen's win is not impressive, but it's hardly unusual those times. We even had teams like Steaua, Red Star winning UCL those years (in fact Steaua played two UCL finals in a span of 4-5 years).