The 2020 INEGI (federal) census counted 44,415 men and 44,221 women for a total island population of 88,626. People tend to overestimate the island's population. By the official, federal and state, door-to-door headcounts over the years, it has never been as much as 100,000.
I think comparing Cozumel's per-capita murders with other, much larger cities is worthless. You need to compare Cozumel's murder rate with the murder rates of cities that have a similar population to get a valid comparison.
I also think the idea that "it is only happening to drug dealers" is ignoring the possibility of innocent bystanders eventually being wounded or killed by these wild sprays of bullets. These aren't experienced hitmen putting a gun to the back of the head of a target. These kids tend to empty their firearms completely, with only a few bullets actually hitting the target; the rest go wild.
Time of day and distance from the plaza are not factors in where these assassinations took place. They happen during the day as well as the night, and inside the Centro and outside the Centro. Hemmingway on the Malecon, Chedraui by the police station, Tentaciones Restaurant on 15th, are just a few that come to mind that happened inside the Centro, and two fo those were during the day.