Smartphones make it easier to optimize your transit lines on the fly, sure (yet I'll note the practice existed before smartphones). But there are different philosophies to traveling: some leave at the last possible minutes and ponder the optimal route choice while running to the bus stop. Others aim to be fifteen minutes early, stroll leisurely, watch the scenery and get lost in their thoughts. I suspect someone who likes a dumbphone to be the latter type.

Being a different type may change the frequency of each situation, but stuff happens so anytime can be in these situations.

Really having a smartphone does not mean you need to use it for much. IMO, the jump to cellphone vs not having one is a bigger downside as someone can call ar any time interrupting your thoughts. But even you can just turn them off, while still benefiting in an emergency.