They suffer more issues from lack of use rather than high use.
This is true, our fleet was utilised 7 days a week, probably averaged around 3-4 hours a day, the private larger aircraft that sat around tended to have more issues. Only about a third of the aircraft had Continentals though and they were problematic turbocharged ones that really struggled to make TBO. The only engines I remember on the exceedence program was the Lycomings and when the airwork aircraft went on condition one of our 0-320s made it to 2500hours, it cost a fair bit more than the others to overhaul though. Not sure what the record for keeping them going is, that was a 4th or 5th life engine as well.
I havn't had the pleasure of dealing with many 520/550 engines other than using them, most of ours were lower powered.
Also looks like after reviewing the PDF there's no "new" technology, just the cumulative effects of introduced technology since 1960. Looks like most of the new TBOs just come up to match what Lycoming already has out there.