Liljegren was gifted copious amounts of time on the PP - including the top unit - both all through last year (I watched him at least a dozen games last year and he was always on a PP unit, generally on the 1st PP), and through at least the first half of this season. He played himself out of a role getting significant PP time.
44.4% of Liljegren's career AHL points (regular season and post season) have come on the PP (16 PP points and 20 ES points in 109 career games). 43.8% of Sandin's career AHL points have come on the PP (14 PP and 18 ES points in 46 career games).
I am not talking about last year.
This year, Rosen was on the top PP unit since the Oct 5th opener. At no point did Liljegren get more than a shift or two on the top unit PP at a time.
You wonder how different the season would have turned out if he was simply handed top unit PP time, like Brannstrom in Chicago (or Sandin here, after Rosen moved up and Liljegren was injured).
This year, Liljegren was on the second unit sharing time w Sandin until his injury. Those are the facts. Liljegren was not given a run on the top PP unit this season, despite any narratives you might be trying to impose.
Since that point (two consecutive ankle injuries), his season has been essentially a writeoff from a production point of view. The main thing for his development is that he is on the ice playing, and slowly recovering his elite footspeed/skating.