Lets see now, in the last decade or so the diesels have had to contend with tighter and tighter emissions standards such as NOX and particulate matter, much lower levels of sulphur lubricant, diesel particulate filters, diesel oxidation catalysts and now corrosive diesel exhaust fluid systems while the rules for the gas burners are virtually unchanged.
The complexity of the diesel is much greater than a decade ago, while in the same time frame we been finding interesting ways to extract more and more power from the gas burners with no hit on reliability.
Both have gained significantly in output over the years but I would have to predict that the newer diesels have lost a bit of their long term reliability in the process.