The moment you add anything that isn’t mentioned in DJI’s list of authorised accessories (page 86 of the Mini 5 pro manual) it takes the drone outside of the certification scheme and it becomes legacy so if over 250g is limited to flying away...
Pretty sure that is not correct. Yes you can fly a C1 marked drone in A1, so Air3 S, but not an unmarked drone above 250g but below 900g like an Air2, so no, the Mavic Pro, a legacy drone, is sent back to the countryside.
If that had been made...
Not true, the Mavic Pro has a precision landing system. It just isn’t as developed as later drones but with a landing pad was certainly capable of landing within inches of its takeoff point.