This works sometimes, but there are also a lot of cities with public transit systems that are split into multiple providers. So you might have one website that shows you the subways and trams, and a different for the buses and regional trains. Trying to plan a trip with multiple connections can become quite difficutl very fast then. Especially if you are trying to do it on the spot instead of having had the time to plan in advance.

Potentially, yes, but the official apps available are all using Google Maps ... so I'm not sure how much of an improvement that would be over just using GMaps to begin with