While we're talking about Taz: I think early overuse broke him, but as his workload was actually pretty reasonable, I don't think Farrell is to blame for not anticipating his decline.
Through the end of May, Tazawa got into 22 games and pitched 20 IP. He K'd 26 and walked 5. He allowed 13 hits and 5 runs, for a 2.25 ERA. 9 holds and one loss. A .500 OPS allowed. 1 HR (0.45 per nine). That's a heavyish workload, but not too heavy, and excellent results. He has pitched as many as 68 IP in a season as a reliever, and through April and May, that put him on a 60ish IP pace.
Since May 31, he's thrown another 25 2/3 IP in 27 games. His ERA has more than doubled to 6.31 as his OPS allowed has almost doubled to .916. His home run rate has sextupled to 2.8/9. Yikes.