In Ovi's best seasons:
2007-2008 = 6% lead over #2 in points, and 25% lead over #2 in goals
2009-2010 = 10% lead over #2 in points/gp, and 10% lead over #2 in goals/gp
McDavid:
2016-2017 = 3% lead over #2 in points/gp (Crosby missed 7 games), 32% less goals than #1
2017-2018 = 6% lead over #2 in points, only 1% lead over #2 in points/gp (mackinnon missed a few games), 16% less goals than #1
2018-2019 = 4% less points/gp than #1, and 20% less goals than #1
In total, McDavid has never had a relative point advantage as peak Ovechkin did, let alone the goalscoring dominance added to it, Ovechkin was also going up against young and dominant Malkin and Crosby.
As far as total points go, it's essentially a wash as Ovi in 2009-2010 was on pace for 124 points (he missed 10 games), and was on pace to lead the league in points by 12. Whereas McDavid last year was on pace for 122 points, 6 less than the league leader. League scoring was also up last year compared to 2009-2010.