Honestly I can't imagine feeling that a 70 minute connection on an all-DL itinerary was "too tight" but somehow a 1:45 connection on separate tickets WN-DL was just hunky dory. That's crazy.
Agreed. A 70 minute connection on a once a day flight would feel tight. I'm with the OP there. But turning it in to a 100 minute connection that also requires switching airlines which means giving up misconnect protection... that's going completely the wrong direction for cost/benefit.