Organic stats that occur from the natural progression of sport are less flawed than manmade statistics. A manmade stat, more aptly called a 'metric' or 'formula' or 'algorithm', is inherently more unreliable because it is created by man, who is inherently flawed. A double is a double because you see it is a double. To understand WAR, you have to read a long, convoluted explainer. There's a large difference there.
Blowing saves is not doing one's job correctly. Especially when ones job is "closer." Whose job is to "save" games. Mental gymnastics cannot wiggle out of that one.
So there is no trend, by your own admission. Which means there is not a positive trend either. Which should be disconcerting, at $20 million per year. One should expect a positive trend considering his supposed pedigree, and his current pay grade.
Diaz ranks 18th out of 29 in save percentage since joining the Mets in 2019, among pitchers with 50+ saves. That means he's done worse than ~61% of those on the list.

Among pitchers with 100+ saves since 2019, he is SECOND-TO-LAST in save percentage. He has been the second-worst closer since 2019. Since a closer's job is to save games successfully.
