Any number of ways - I may spend some of my vacation time doing absolutely nothing at my home. But, for us as a family, being in our car driving someplace new and/or fun, the vacation starts when we leave the driveway. For me personally, it starts when I pull out of the parking lot at work

When we are on a destination-type vacation, that doesn't mean we don't also enjoy all that the states "in between" have to offer
Fair enough, but I also left out lag time. I assume if you're the first off the plane and jump on that bus, the bus doesn't pull out within seconds. There is time used in that step.
True, but it's about equivalent to stopping for lunch and a bathroom break, which a driver will do many, many times over each way.
Park tickets for "extra days" are much cheaper than the resort stay for that time, so we'll forget that one from a budgetary POV. As for the vacation time, well that depends on how long you plan to stay at Disney. If you want 7+ nights, then yes you do have to take more time off work (assuming you're not in a profession that has Summers off,
like my wife). If you're only planning to be there 6 or fewer nights, you can accomplish that whether flying or driving with exactly the same amount of vacation time.
This explains a lot.
In OP's case, there's no real way to be in the park Saturday morning. OP has a 3-hour drive just to get TO the airport. He may very well have to spend Friday night in Dallas in order to take a Saturday morning flight, or leave home at an insanely early hour that would make Saturday pretty much a waste anyway.
This is where the time spent being able to fly will really vary depending on where you live. Philly International is around 1/2 hr drive for us, AC about 45 mins. Getting to an airport doesn't take long but still the more stressful part of travel for me. If I could take a helicopter from my driveway to PHL, I would.
I have zero problem getting home late Sunday and being at work Monday. I wouldn't be any less exhausted if I flew home Sunday than if I drove home Sunday either.
My dh could easily get home late at night and go to work the next day. He neither unpacks nor does all the post-vacation laundry. In fact, vacations are a breeze for him. 
you must not have a long drive then if you could leave WDW on a Sunday then be at work Monday.
Shoot, I get 3 weeks, 1 of which is set aside for Christmas week whether I want it or not. And I still drive EVERYWHERE we go. Speaking
for me (since you asked), time with my family is precious whether in the car "to somewhere" or if we're already "somewhere".
There is no amount of money you could pay me to fly anywhere within a 10-hour drive. At best, I'd break even. I've had far too many of what would have been 4-8 hour drives turn into 8-16 hour "flights" in my day due to the inevitable delays. Blech!
Our max drive would 6-8 hrs. For us what should be a 6 hr drive, let's say to Williamsburg, easily turns into an 8+ hour drive due to traffic, construction, etc. No method of travel is without delays but in the 30+ vacations we've taken by air, only around 3 stand out as having more than a 30 min. delay. Maybe we're just lucky. OTOH, every time we drive, it's a PITA. By the time we hit VA, I remind dh that if we were flying to FL, we would have been there already.
We always seek out interesting places to eat along our route. Sure, there's the occasional sub sandwich (we've long ago figured out how to keep them dry), but we have nice sit-down meals as well. Even fast food places we don't have at home (like Zaxby's) are a bit of a treat on vacation
Still, having a leisurely table service meal will only add to your total travel time. Something a flyer doesn't have to deal with.