Yeah that's the difference. Aberdeen could have had this type of season in other years when Celtic have 'only' got to 80-something points. But right now they look set for somewhere around 100 points which is going to be almost impossible to keep pace with.
It's a reflection on the squad and the types of managers we have had. All the recent Rangers managers were good at playing organised, compact, ball-retaining football that takes you far in Europe, but isn't that helpful for the domestic game. The squad was similar with a load of competitive, tidy, hard-working midfielders, as well as transition-specialists like Kent and Morelos who came alive in Europe. Kent in particular struggled against deep-lying domestic defences. For Celtic however both Rodgers and Ange specialised in attacking overloads and high chance creation against weaker teams, which is ideal for racking up goals and points in league matches, but leaves you wide open against real quality in Europe.