I opted for unloading over dumping because I didn't want to deal with the hassle of constantly unforbidding everything.
Oh... the track stop dump just takes the Desired Items from the cart and piles them up on the ground.
This is wrong. The dumping track stop fully empties the cart, it expels
everything. It's an autonomous mechanical contraption which doesn't care about settings of a route stop that may happen to be in its location.
And "desired" items at an unloading track stop define the items that should
remain in the cart. Setting those you want unloaded guarantees a complete and utter malfunction, because the setting's very purpose is to
prevent their unloading. Of course, this only matters if you unload by hand, because - see above - route stops and their settings have no influence on track stop dumping.
The other part is right - dumping by track stop doesn't forbid items.
I also realized that my Dorfs were taking the super scenic route to reach the start of my mineshafts, because they deemed that walking on tracks is dangerous.
They do not automatically deem it to be dangerous, you need to make the walk path more desirable than the track path.
Tracks
are considered more dangerous by dwarfs - the carving/construction of the track automatically marks it with a "low" traffic designation (pathing cost 5 vs. 2 for "normal"), meaning dwarfs will prefer a non-track path to get to a location even if it's twice as long. Of course, if the non-track path is three times as long, dwarfs will walk on the track (assuming low vs. normal traffic designations).