I think Copa and Avianca, TACA/LACSA, in the old days, tend to be pretty conservative in their schedules as well. E.g they pad the flight duration. Makes the schedule easier to meet or beat.
Every (long) TACA flight I took arrived early, sometimes as much as a hour.
Add airports like PTY and SAL as hubs where passengers go gate to gate with no formalities it's not hard to see awards won like this title.
COPA seems to be fairly good in assessing loads and wheelchair passengers as to boarding times so departures are mostly on time or early.
COPA will hold flights where they are limited to daily or less. I waited an hour on PTY YYZ due to a late inbound from Buenos Aíres and with no flight the next day to YYZ, which beats handling passengers who'd have a two day delay.
COPA could be even more efficient with decent signage in PTY and employees that actually know how to drive the sky bridge to the aircraft door. 15 minutes on the 7th. Of actual moving it.