For various reasons, we emphatically disagree even with the proposition that it was the UK's largest ever democratic exercise.
We put to one side defective conduct of the referendum - which suppressed much of the Remain side - but here focus on two factors: voter turnout and lead of the winning side expressed as a proportion of the electorate.
Turnout in the 2016 referendum was high at 72%, higher than the 65% turnout in the 1975 referendum.
However, since 1945 there have been 13 General Elections with higher turnout:-
Winner as share of the electorate
Nor was the margin of victory in the 2016 referendum large, defined either as a majority over the losing side or as the share of the electorate on the winning side.
The chart below shows elections and the 1975 referendum since 1950 where the share of the electorate supporting the winning side was greater than in 2016:-
The two front-runners are the 1975 referendum and Labour's result in 1951 (when a Conservative Government took office on fewer votes than Labour won: a bit like Trump and Clinton in 2016).
The chart below shows that the difference in the share of the electorate between winning and losing sides was more than 8 times greater in the 1975 referendum than in that of 2016:-