I am of two minds about this.
On one hand I don't have many objections to his in game moves. The best players will play in ~150 games, and the best bullpen pitchers will pitch in ~80 games and everyone is fine with that in theory. But when its time for Josh Rutledge or Noe Ramirez, nobody wants to see that and the manager gets blamed. That comes with the territory, but people had similar complaints about Francona, and I think we all agree he was fantastic.
The clubhouse management has mostly been great. I don't take it for granted that a team can finish in last place, or demote guys with huge contracts, and get nothing but compliance. However, you can't hang your hat on finishing in last place and keeping everyone happy.
The counterpoint is that the results have been terrible. Steamer/ZIPS have projected the last two teams as high 80 win teams, and they have finished in last place. He did manage the hell out of a team full of veterans to a world series, but the year before that he lost 89 games with a roster than was expected to compete. Other than 2013, none of the veterans he has managed have really overachieved, in fact last year almost all of them were complete disasters. Even more damning is the performance of his rookies. By my count, he has managed 8 consensus top 50 prospects, and the only one who has stuck in the majors as a full blown top talent is Mookie Betts, who is off to a terrifyingly bad start, with cratering underlying numbers.
Taken individually, I can't find a reason to blame him for a single one of these things, but together it is a shoddy record.
Tonights loss starts a run where they should really clean up. The Rays are talented, but seem like the worst team in the division. The Yankees and Astros are decent teams. They get 4 games against the Braves, who are absolutely awful.
I dont think being a game under .500 right now is a disaster, but they need to be better than that at the end of the month. Sometimes coaches get fired purely because the team performance isn't good. Not everyone has to be a Bobby V level clusterfuck. Farrell seems ok to me, but it would be hard to complain too much if he gets canned, considering the results.