The prince is so dazzling~
I was expecting something like turning it a magnet train, but that might be jumping too far ahead. I think the slope system is neat, but indeed it has some practical issues like emergency stops.
Still, as the first train in this world ever I think it's decent. If it's fine once it builds up speed, then emergency stops are rare enough for it to be chalked up as a delay. And I assume the crafts guild can handle replacing the parts that are damaged by said friction.
Pulling the train up the slope is essentially "reloading" the potential energy for the next departure, but I see it as just some more job creation. If the crafters are risking their lives on the walls and as adventurers, then surely the manual labor of pushing/pulling a train would be preferable.
I'm also imagining a system where the train is attached to a pulley and people just climb the tower carrying counterweights for the other end.