It's funny how two different people can draw two very different conclusions from the same study. Autoblog did an article on that very same University of Michigan study and concluded that total cost of ownership was lower for diesel vehicles over the longrun, primarily due to fuel savings and higher resale values:
https://www.autoblog.com/2015/07/17/diesel-gas-total-cost-ownership/
The article you quoted was analyzing things from the fleet owner's perspective, which is likely a bit different from a private/individual owner.
The common definition of an investment is: an expenditure of resources (usually cash) with the expectation of future
returns or profits. Seeing as how no one actually makes money through buying a regular car (obviously there are exceptions such as rare or very old vehicles), I'd argue that in the traditional sense a car purchase is not an investment. But if you want to forget semantics and pretend that buying a car is an investment, even you seem to realize that it isn't a good investment, as it is
losing value the moment you "invest."
Operating costs are important, and I'm even willing to acknowledge that certain maintenance costs will be higher for a diesel vs a gasoline rig. However, I think you and others on here owe it to yourselves to actually calculate the those costs rather than throw out vague guesstimates. The issue is when it comes time to sell your depreciating asset (the vehicle), what will be the difference between the two in the money recouped from the sale? And what will be the difference in total fuel costs?
I've seen what both engine types will return in real life and the math I've done shows a distinct fuel savings advantage for the diesel in most driving situations
that I encounter (to the tune of ~$1k-$1.4k a year). I suppose YMMV depending on driving habits, towing, modifications, traffic, ect. Do you suppose that the additional diesel maintenance costs per year will come anywhere close to negating that fuel savings? Based on what I've seen and figured, they don't.
As for resale values, I regularly see 10+ year old diesel Ram 2500's fetching a $6k-$7k premium (sometimes higher) over comparable gasoline trucks, and mind you the difference in original MSRP's between the two wasn't as great back then as it is nowadays. I guess time will tell if the newer 6.7l Cummins and 6.7l Powerstroke will have similar premiums 10 years from now. Also keep in mind, that the advertised MSRP and factory pricing for diesel trucks, or any truck, isn't the same as what the product actually sells for on the market. There are normally dealer incentives and negotiated pricing for those trucks. Just because Ram or Chevy advertises the diesel engine as a $8k-$9k option doesn't necessarily mean that there will be an $8k-$9k sale price gap between new diesel and gasoline trucks.