Dermott played 87 regular season AHL games, plus 26 playoff games.
Liljegren has played 44 regular season, and 20 playoff games in the AHL already. Half a season in the AHL, and he'll be on par with the amount of time that Dermott spent there. I'm not saying that they are on the same path, but it wouldn't be a complete shock to see him up at some point. But, that's solely based on his readiness.
14 of those AHL playoff games for Dermott were also after the call-up. Including both regular season and playoffs, Dermott had played 97 AHL games before being called up to the NHL for a two game stint, and then 2 more AHL games before being called up for good.
Lilly has played 64 AHL games, and when you add in the SHL games he has played 102 games of high level pro hockey.
Dermott was a great D in the AHL. But he wasn't dominant. Nor was he dominant when he returned to the AHL for the playoffs. That shouldn't be a surprise. Few D are dominant at the AHL level.
Dermott was also 21 years 15 days old for his NHL debut. Lilly won't turn 21 until April 30th 2020.
Dermott was a second round pick who has improved a lot. Lilly was a mid-first round pick who had been pegged as a top-5 draft choice at the start of draft year. Since his draft he has shown that he is better defensively than he was given credit for. His offensive numbers were not what most people expected. However, as I have said, he started off the year with 5 points in 7 games, and then as far as I can tell (and the interviews seem to support this) shifted heavily to concentrating on improving his defensive play and other aspects of his game. I feel that this constant concentration on those aspects of his game led to him essentially choking offensively (ie your timing is a little off etc because you are not playing naturally - because you are focused on changing other aspects of your game). This year will likely provide the answer as to whether he is simply not as good offensively as he was advertised, or if he comes into his own.
Beats me when Liljegren will called up. The Leafs have more D options on the right side than they did a year ago (Ozi, Subban, and Holl - who improved significantly last year). None of those options are top-4, but they are still there.
However, people saying that he should be baked until he can enter the NHL in a top-4 role are dreaming. Babcock is going to shelter the crap out of any young D entering his lineup, unless it is a catastrophic multiple injury situation.
I think that the baking philosophy is essentially nonsense. I haven't seen examples of players coming into the NHL and playing top line/pairing roles because they baked for years in the AHL. It wouldn't have turned Luke Schenn into a different type of D. He was simply a dinosaur pick by dinosaur management entering a league that was rapidly changing away from valuing those types of dinosaurs.
The stature of Swedish prospects, especially D prospects, has grown tremendously over the last decade or so. It seems to not support the baking philosophy either. Prospects are pushed up to higher leagues quickly, like the SHL, at young ages, where they get limited ice time and are often the 7th D (they play with 7D in the lineup there), but do get experience playing at a higher level and learning from better teammates. In North America Strome sat in the CHL for years, not good enough for the NHL, not challenged in the CHL, but not eligible for the AHL. I think that was disastrous for his development.