It's really not hard to beat. Brian Clough's Forest took the English domestic league title from the best team in Europe (Liverpool) having only just been promoted to top flight football, then knocked them -the holders- out of the European Cup in the first round of the competition the following season before going on to win and then retain it. Meanwhile they appeared in the League Cup final 3 seasons running.
It is when you consider the following;
Aberdeen had never even got to a QF in European football in their history before or after SAF
Since SAF won the title with Aberdeen, only Celtic and Rangers have won the title in the last 35 years.
SAF won 3 SPL titles with Aberdeen and they have only won 4 in their history.
Since the SPL began in 1890 (111 years), their have only been 18 league titles not won by Celtic and Rangers.
Only 3 clubs have won the SPL more than 3 times in their history that are not Celtic or Rangers. These are; Aberdeen 4, Hearts 4, Hibs 4. Of these 12 wins in 110 years, SAF has won 25% of them.
SAF winning 3 SPL titles with Aberdeen is therefore harder than Nottingham Forest only winning 1 English top flight league title.
Aberdeen had to beat Sion, Dinamo Tirana, Lech Poznan,
Bayern Munich, Waterschel and
Real Madrid to win the Cup Winners Cup.
Nottingham Forest won their 1st EC by playing
Porto, AEK Athens, Grasshoppers, Koln and Malmo.
Nottingham Forest won their 2nd EC by playing Oster, Arges Pitesti, BFC Dynamo,
Ajax and Hamburg.
Aberdeen had the more difficult teams to beat than Forest. A team as tiny as Aberdeen going on to beat Bayern and Madrid on their way to the Cup Winners Cup is ridiculous.