You wouldn't *have* to stay overnight at AMS unless you really wanted to; on the days that KL flies to MIA (and it's only 3 times weekly, on Sundays, Tuesdays and Fridays), the flight leaves at 10:25, which means you can leave the same morning on most of the first wave of flights from Scotland (e.g. first flight from EDI leaves at 05:50, first flight from ABZ leaves at 06:00, first flight from GLA leaves at 06:05) leaving you about 2 hours to make the simple connection at AMS. From INV, it does indeed appear you'd need an overnight stay.

You might have a bit of a longer wait at AMS on the return, but my vote would be for AMS over LHR.

You don't have to clear security or passport control at AMS when connecting from non-Schengen to non-Schengen.

The issues with AMS are mostly for passengers originating in AMS - transfers are unaffected. Also...it's highly unlikely that either LHR or AMS will still be seeing the current chaos in November - if only because travel volumes will be much reduced in November compared to the current summer travel peak, and presumably they will both have found and trained more employees by then.