Lack of technology would be my guess for the F100. We're talking about an airplane that was made in the 1980's. I reckon an iPad running Ozrunways is more advanced. Use that to get your JULIM / BEVLY estimates!
90s for the Oz aircraft I think? But when the regular industry users of these geriatric aircraft ask for newer more reliable ones, we are told condescendingly by the airlines operating them “they were very advanced when they were made and stand up well against today’s modern jets”
Regardless of type, any professional pilot who can’t make good a time over a fix should be sent back to school.