Injuries, lockouts, and a coach that sabotaged his PP production have really cut into Matthews' production so far.
That being said, he was only 20 goals back of Ovechkin by the end of their age 23 seasons, and with Ovy scoring 50gls in his age 24 season, Matthews is on pace to cut into that lead by the end of the year. (By about 7 goals or so at his current pace).
The annoying thing of course is that Matthews has outscored Ovy at even strength by a good margin at the same age, but Ovy benefitted from getting more than double the PP time - 5:49 pp time per game for Ovy compared to only 2:42 for Matthews at the same ages. Part of that is that the Leafs don't get much PP time, part of that is that PP time was way up league wide in those first few Ovy years, and part of that is that Babcock sabotaged Matthews' PP time.