The Toronto Maple Leafs finished last season by using Pontus Holmberg more or less as their 3rd line centre after they promoted Max Domi to the first line to play with Auston Matthews.
Now, Max Domi was an abomination as a third-line centre, so when Toronto Maple Leafs ex Head Coach Sheldon Keefe inserted Holmberg in Domi's old spot, it was an improvement overall.
It's not Keefe's fault that the Leafs didn't have a better option on their roster, or that their GM decided to mostly sit out the trade deadline.
The Leafs finishd the regular season using a 3rd line of Robertson-Holmberg-Gregor which should have been, but wasn't their fourth line because Ryan Reaves was playing with David Kampf. The Playoffs were a mess because of all the injuries to Nylander and Matthews, but game 7 saw Holmberg playing on a line with Auston Matthews and Calle Jarkrok which was EXTREMELY ineffective.
So, all that being said, Pontus Holmberg cannot play 3C for the Leafs this up coming season.
The Toronto Maple Leafs Can't Use Pontus Holmberg Higher Than the 4th Line
In 54 games last year, Pontus Holmberg's 5v5 numbers were great. He posted a 51% Corsi and a 53% Expected Goals rating while the Leafs won his minutes by 59%.
Considering his most common linemate was Ryan Reaves, his numbers are great. The Leafs should definitely want to use him this year, just not as their third-line centre, or preferably, not above the fourth line.
In fact, with his league minimum contract, great defense and potential upside, the 25 year-old former 2018 draft pick is an excellent choice for a fourth line role that can potentially grow.
Holmberg provides solid defense and his scoring is underrated. He is nearly a career point-per-game AHL player and thus an obvious NHL player. He scored at a rate of 1.7 points per 60 last year which is only slightly below the rates of John Tavares and Tyler Bertuzzi. (All stats naturalstattrick.com).
Holmberg has potential, but the Leafs can't have him in their top nine because his ceiling in the NHL is third line centre and he's not yet reached it.
The Leafs have a lot of options at 3C - they can move Marner to centre and use Tavares lower in the lineup, or they can revert to Max Domi (bad option) or they could promote David Kampf (horrible option) or, most likely, bring in someone via trade to fill the role.
Using Holmberg there should not be an option. He is, however, a great replacement for David Kampf who must be traded before the season starts.