I'm just going to point out that McAvoy just turned 21 in December while Krug turns 28 next month.
During his 20-21 year old season, Krug was in his final year at Michigan and would see 2 NHL games so he could burn the first year of his ELC.
During his 21-22 year old season, Krug saw 1 NHL game in the regular season and 15 playoff games where he scored 4G and 2A.
Prior to his 21-22 season (which will be next year so it doesn't even count whatever he puts up this year), McAvoy has already scored 1G and 7A in 18 playoff games.
To assume McAvoy's 0.5 ppg pace average in the regular season and slightly below that in the playoffs won't improve, is crazy. The average NHL player peaks at age 27 (Bergy and Marcy not being average) so this is probably the best Krug will be. McAvoy is still 6 years away from his peak season!
Will he be a #1 PP QB? Yes. The main problem is that PP1 has been tuned for LD while McAvoy is RD. Additionally, the Bruins load up PP1 so PP2 doesn't have the same high end offensive players on the ice.
My concern if the Bruins trade Krug is not the PP, but that they should get a top 10 pick AND a high end prospect in return for him.