Lessons here for delays on any airline...

• Get in line at the "service desk" if you must but get on your phone to an agent at the same time. When you finally get to the head of the line, there may be few options for a timely rebooking. Better yet, use the app. It should have provided some options.
• Have some kind of travel insurance, either the stuff they pitch with the ticket, or via a credit card. It can help with overnight accommodation and other expenses in these situations.
• If you misconnect due to a mechanical delay, ask for meal vouchers or whatever. You should have been able to get something in SLC given the maintenance delay on your LAX-SLC flight.
• Don't waste your time at the baggage office at your origin unless you need to retrieve your bag. Standard airline practice is to load the bags on the next available flight. No reason to wait in a long line just to hear that. Note that the bags may not follow your exact rebooking but they will get to your final destination. Use the app or Airpods to keep track of the bags.
• If you write a long letter to the CEO make it clear what you want in compensation. It sounds like they already gave you some SkyMiles. You got to your destination. What else could DL do?

It certainly must have been frustrating, but the reality of air travel today is every bit of this story happens all the time. Best to be prepared with the right tools and information so you don't need to rely solely on the kindness of strangers at the airline. If you had started a thread on the afternoon of Aug 18, when this odyssey started, instead of a week later, you no doubt would have received a lot of useful advice in real time.