I think what the OP is trying to say is the following (correct me if I'm wrong):

Looking at EWR - YHZ - EWR the following observations can be made:
EWR - YHZ: 1:57h flight time
YHZ - EWR: 2:07h or 2:33h flight time*

Note the increase of flight time on the return leg

Then looking at:
EWR - YQB - EWR
EWR - YUL - EWR

*The same 'increase/padding' of flight time is not seen on the YQB - EWR and the YUL - EWR legs, despite same aircraft, same inbound airport (EWR), same carrier, same inbound arrival times (afternoon).

The OP is trying to understand, why only the YHZ - EWR leg has so much additional flight time / padding. The OP's understanding is that if it's additional padding and/or congestion, then why don't the other legs have similar padding scenarios?

@Saxman66 provided a rationale response that the 'wind doesn't affect north-south routes as much...'