Some folks insist that the problem had to have been with the players (Jeimer, Schoop, et al.) because they hit decently in 2021 and collapsed in 2022, and we had Scott Coolbaugh here for both.
To your point, a player doesn't need the hitting coach to step in and fix things when he's hitting well. The player needs the hitting coach to step in and help him when he's struggling. Apparently, Scott Coolbaugh was a fine hitting coach when he didn't have to actually coach.