The challenge with evaluating drafting skill, is that it generally takes 3-4 years, and often in that time, personnel have changed.
To me, the "criteria" for "drafting well" are twofold.
1. In the 1st round, are you consistently "hitting" on your first round picks (and to a lesser extent, early 2nds), and if you don't hit on a given year, are you "missing"? or is it just a weak "range" that you're in?
To evaluate this, you've gotta look at the Liljegren, Matthews, Korshkov, Marner, Dermott, and Nylander picks.
Liljegren: So far hasn't shown anything. The jury may still be out, but at 17th Overall, it does appear that the Leafs missed some pretty good players in the form of Josh Norris, Robert Thomas, Filip Chytil, and Kailer Yamamoto who were all drafted 19-22.
Matthews: No brainer pick, so points for not overthinking it I guess?
Korshkov: Obviously he hasn't given the Leafs anything... as the 1st pick of the 2nd round, I can't help but feel disappointing with Jordan Kyrou, Alex Debrincat, Samuel Girard, Carter Hart, Ryan Lindgren, Filip Hronek, Dillon Dube all also going in the 2nd round.
Marner: Somewhat of an easier pick (not on the same level of Matthews), but I think the Leafs do deserve some credit for not overthinking it, and getting a player that is at worst, amongst the group of Aho, Rantanen, Barzal who would all arguably be the 3rd best player in the draft class.
Dermott: I'd rate this pick as "good"... they got a bonafide NHL player, but I'd stop short of excellent, given the talent that was available in the 2nd round that year (Aho 35, Carlo 37, Cernak 43)
Nylander: I think the Leafs deserve a huge amount of credit for this pick. Yes, it's probably a toss-up between him and Ehlers, but the contribution level really drops off after those 2.
Overall, In the top of the draft, you've gotta give the Leafs credit, they're not making mistakes (such as Boston with Zobril/Debrusk/Sensyshyn, followed immediately by Barzal/Connor/Chabot), and have certainly hit on 4 of the 6 picks over those 4 seasons; but they're also not really being "challenged". 3 of the picks they hit on were in the top 10. To be considered "excellent", I'd want to see more consistency in "hitting" outside of the top 10.
2. In the later rounds, are you regularly getting career-NHL players.
By career-NHLers, I think you have to look at guys who last in the NHL more than a year or two.
In this criteria, there seems to be a noticable drop in what the Leafs have gotten over the last few years.... going back to 2011:
2011: Josh Leivo
2012: Connor Brown
2013: Andreas Johnsson, Carter Verhaghe
2014: Pierre Engvall
2015: None
2016: Grundstrom, MAYBE Brooks
2017: Seemingly none
I wouldn't consider the above list impressive... especially since the best guys (Brown, Johnson, Verhaghe) were all 8 years ago now.
Overall, the Leafs deserve credit for not screwing up or botching high picks, but they really haven't done much to write home about beyond that. Even if you look further back at the 1st round, its a similar story. Flop on Gauthier (21st), hit on Rielly (5th), Flop on Biggs (22), Flop on Percy (25), hit on Kadri (7), hit on Schenn, sort of (5th).
I'm don't believe you can say "they draft well", but I also wouldn't say they draft poorly. If anything, they draft poorly considering the resources they have.