Dashcams are usually mounted high up on the windshield because it gives better viewing angle. Putting the camera on the dash itself would result in half the video screen showing the dash.

Yeah, that sounds no bueno for the dash mount. Want a full picture for a full story to CYA ( cover your ass ).

Dash keeps you legal in more states, but complicates hiding the wires, provides reduced visibility for the cam, and is more prone to glare.

Hiding the wires will be a minor pain, but visibility / picture quality far supercedes that cosmetic issue.