And yet the people most glued to their device-dopamine loops are the ones most likely to be ambling along...

The problem isn't really slow walkers (etc), but rather the ones who are in the way due to not paying attention and seem to justify it by thinking everybody should just walk as slow as themselves. One can be slow and considerate, just like one can be fast and inconsiderate. The latter mainly just comes to a head with people walking opposite directions though, for obvious reasons.