It's a pointless statement because apart from maybe 2-3 teams in the league (like the Braves), every other team in the league will have had at least one stretch at some point in the season wherein they "underperformed their ability". There are teams currently behind the Jays in the standings who would have just as good a record (or better) if not for a bad stretch earlier in the season, so this logic doesn't only work in one direction. But it's only ever brought up from the perspective that it somehow doesn't apply to the teams behind the Jays as well.
Did you guys know that from May 7th to June 8th the Red Sox went 10-18?
If they managed to play even just 14-14 over that stretch, they would be sitting at 64-51 right now and one game back of the Jays. They were actually 21-16 on May 7th, and after June 8th they were 31-32.
The Jays' season doesn't operate in a vacuum. "Coulda-shoulda" logic applies to everyone, hence it serves little actual value.