The issue with this reasoning is yes- Disney chooses that time assuming the worst case scenario: A family who probably doesn't fly much, has to wait in line to check bags, probably has a stroller, and doesn't have PreCheck, so that there is no issue with every DME passenger making their flight. Many of us aren't in that scenario - I'm usually flying alone, will have just a carry-on, am an elite member (so if I do have to check a bag there is little to no line), and have Clear and TSA PreCheck.
These days, I usually just take Lyft to the airport, but when I used to take DME, I would give a later flight than the one I was scheduled on every time.