A4 has a visibility problem

When interacting with a waypoint, you can see where you haven't been.

No such QoL when sailing using the boat. Very annoying and very easy to implement the waypoint equivalent.

Yeah I agree, waypoint in POE1 is very clear what zone you have entered. It's not a big problem, but it is less obvious which zones are cleared, if rewards or waypoints haven't been tapped, and since it is less linear in areas, it can be less obvious where player has gone. As you are saying, act4 is an area which is not linear, player can go to many options of islands.

I would add to this also that I think some times when using the travelling mechanic, it does not initially show the zone level, which is important when you have options, as you may want to start with the lower level zone. I think act4 does do this, but it might be act 2, where it does not initially show the levels.