They had elite number one centres on their top 2 lines and the third line had probably the most overqualified centre in the NHL. The 4th line, however, was a totally different story with Frederik Gauthier and Par Lindholm being the primary centres. Considering all the offensive talent the Leafs had down the middle, their worst two shooters centred the bottom line.
The 2019-20 season will be completely different. There was too much talent to go around last year and that resulted in Tavares and Matthews simply not playing the minutes they deserved.
This coming season there is no Nazem Kadri for the third line and the likely replacement is one of the new recruits, Alexander Kerfoot or Jason Spezza.