A 40 minute connection in ATL is not "aspirational" - it's completely normal. If "50%" of 40 minute connections were resulting in misconnect, they would be changing the MCT.

I book 35-40 minute connections in ATL all the time, and the last time I misconnected was 2015 - and in that case it was a WX irop, and my original connection was over an hour.

The idea that these are insanely dangerous connections is simply ridiculous. Delta has no interest in booking unrealistic connections, as this is effectively spoiling their perishable inventory. MCTs are set with this in mind.