All these things are true, but also not true. Girardi has added little value, arguably negative value, but managers rarely matter more than the talent of the roster. And this is the same club Klentak built, and the same .500 team in need of a few breaks that nearly everyone thought it was before this season. The entire premise of the franchise is that the talent was already there, and just needed a better manager and a better bullpen. That premise was wrong. Other than Bohm, the injuries and declining performances are to be expected when your entire core is free agents. The bullpen actually is more than a few wins better than last year but the hitting and defense is worse, so it's wash.
But, Dombrowski's job is ultimately not to make the team watchable or live up to some objective standard of good baseball, but to compete for the NL East title, and this team is no worse than any of the others in that regard. And the things we are seeing this year are happening to nearly every team.
Until then I'd say this team is overachieving, given all the problems outlined in your post. They should be sinking into last place, and they're still treading at .500, though the Mets are defying all their own problems and opening up a little space. Yesterday was a bummer loss, but it was to a significantly better team. We'll see how they do with the Reds and the next homestand; if things go wrong they could be heading for the white flag by the end of the West Coast road trip. If not, and they don't make some big trades/$ expenditures, nothing will change and there's not really even a wild card available.