Size is advantageous in hockey. This is just my read on the situation.
I think there are a couple of narratives at the moment spinning through Leafs fandom. They're separate, but related.
1) Dubas only drafts smurfs
2) Dubas said he wanted to make the team tougher, why did he keep drafting smurfs?
1) is by and large true, but 'only drafts smurfs' is the result and not the reason.
Size is good and useful in a contact sport: associated strength, reach, potential for puck protection, etc. We see prospects who reach physical maturity a bit faster than their peers stand out literally and occasionally on the scoresheet (Lawson Crouse, Nick Ritchie, Logan Stanley, all the Leafs big boys Hunter drafted). The key is determining if their size was the sole reason they had success, or was it a complement to their skills? Prospects that have the skill, speed, and size blend sort of only happen in the top 3-5 range. After that, everyone is a project in some capacity. Dubas' draft philosophy is not looking for smurfs, but he is looking for the skill and hockey sense that is their innate potential. Skating technique and size can be developed over time, but the way the game is processed and the aptitude for quick decision making takes far longer (if not impossible -- see Kapanen
).
Dubas treats size akin to hair colour and nationality in drafting, and it just so happens the most skilled players available are currently smol. He's not averse to size: Justins Holl and Brazeau, Mason Marchment are not smurfs and he plucked them out of obscurity and developed skating and puck technique as much as possible before the asset becomes NHL usable or NHL tradeable. The draft sets the potential meter; the more important development program tries its best to max it out.
2) is simple to answer: only 2-3 picks from 2020 are going to make immediate NHL impact, and it certainly isn't coming from the middle of the 1st round. Honestly, only Lafreniere and Lundell and maybe Rossi should hit the NHL right away. So filling a current toughness need (or any current need, really) isn't coming from the draft.