I have noticed that waiting around on the subway platform or at the bus stop is way more stressful than sitting on the subway or the bus, even if the subway/bus is just stuck for some incomprehensible reason and showing no sign of progress towards my destination.

This leads me to suspect that the stress of waiting for public transit is largely incidental and could be reduced by better station design, without having to make any (difficult, expensive) improvements to service frequency and reliability.