I'd be more concerned with having one of my colleagues pick something up on their way into the office. They're much more likely to spit in my tofu salad than a DoorDash driver.
Christ, dude, where do you work?
I think my concern would be more about the determination being the driver's perception of how good a tipper you are, and thus the need to feel like you need to tip bigger.
And re restaurant vs third party delivery, I'm one of the few people that has never delivered pizzas, so I'm unsure of how it plays out in the longterm. What I can tell you is that gig jobs nowadays, be they GrubHub, Instacart, or Uber, can be incredibly frustrating. Delivering for Domino's means that Domino's is a constant and the customer is a variable. Delivering for Door Dash means both the restaurant and the customer are wildcards, and the number of things that can piss you just increased exponentially. You've got to deliver X number of meals per hour for it to work, and the folks at Potbelly taking too long costs you a tip on this customer
and the ability to get your next, and you don't even know how hard the delivery side is going to be yet. My hunch is that there probably is a greater likelihood of your door dash driver hocking one up in your soda than Mr. Pizza Guy simply because of the greatly increased aggrevation.
Also, since these services probably work better for some places than for others, my advice would be that the next time somebody is in a place that they occasionally get takeout for, ask. I always pick up my own food, largely to support local businesses, and I've had this conversation before. Maybe they'd prefer you order directly, but Grubhub isn't a direct harm to them. Maybe Grubhub is going to put them right out of business. The only guy who knows for sure is the guy that runs the place.