It looks like the Mets are bringing on Eric Hinske as their assistant hitting coach:

Hinske burned brightly and flamed out quickly. At seasonal age 24 he posted a great rookie season for the Blue Jays, winning the Jackie Robinson Award. He broke his hamate bone in his second season, and played without realizing he was injured. His hitting was never the same again.

I can believe the injury may have permanently hurt his swing. However, FanGraphs pitch vales for Hinske show he could only hit the fastball. This is a pattern. Rookies come up, and pitchers see if they can handle the fastball. When the batter proves he can hit that pitch, then the pitchers adjust. Hinske, whether due to the injury or his lack of an ability to adjust, never hit as well again.

There are a lot of levels to coaching, and most coaches are good at some of those and poor at some of those. I would think that for a hitting coach, recognizing when a hitter needs to adjust would be a major strength. There is no evidence Hinske had that strength as a player.