Those comments are full of BS
and the seatmap is outdated too.
J is now 1-4 and 5-6. Different config for LGA
-D and LGE-G.
crew rest used for pax on HEL
day flights. A row is being added as proper crew rests are installed - at least LGG
There are different configurations around the exit rows for LGA
-D vs the rest.
Calling anything beyond row 30 "average economy class seat" suggests to me those comments on that website must be completely fake. The aft section is 3-4-3, horribly uncomfortable and narrow seats.
Anything on 21-30 is pretty good for Y, 21ABC/JL and 22H being the best unless you can score one of those crew rest seats or row 5-6 used sometimes for Y with J seats and Y meals.