Like I said, getting Diaz would be great because he would fill a need today and going forward. He wasn't available for just money in the winter so I'd have no problem trading for him today. What annoys me is the rumor that even if they get Diaz they'd still try to get another guy, or if they don't get Diaz they want to get two guys, when comparable talent was available for just money six months ago. This isn't hindsight. Many people questioned the pen going into the season. Putting Eovaldi in the pen plus adding two new guys that will cost prospects suggests to me that the initial plan was a total failure.
It wasn't a "total failure". They're right in the mix for a playoff spot. Of COURSE it's a down year compared to 2018, but that was by any measure a ridiculously extreme outlier, with very very little chance of repeating. It was much more realistic that this team could win 98-100 games. Right now they're on pace for 10 fewer than that so yeah, definitely disappointing. But "total failure" is a bridge too far. The season still has two months to go.
As others have pointed out, the biggest problem with the pen has been the poor performance of the starting pitching.
Sale is averaging 5.2 innings per start, at an era of 4.26.
Porcello is averaging 5.2 innings per start, at an era of 5.55.
Price is averaging 5.0 innings per start, at an era of 3.66.
Rodriguez is averaging 5.2 innings per start, at an era of 4.13.
As a starting staff, here's their average innings per start (using actual decimals, not thirds of an inning) plus ERA:
2018: 5.4 innings per start, 3.77 era
2019: 5.3 innings per start, 4.75 era
So the workload is similar, though those extra tenths of an inning do add up over the course of a season, but the starters' ERA is a full run worse this year than last.
As relievers, here's their average innings per start plus ERA:
2018: 3.6 innings per game, 3.72 era
2019: 3.8 innings per game, 4.54 era
So they're being asked to get 2/10s of an inning more - that's almost one extra out per game - and of course they're doing it less effectively. So I'm not arguing that the bullpen has been good. They've actually been mediocre at best and bad at worst. I've said for a long time that they need one or two more quality arms, so I'm in agreement with you that it didn't work out. But starting pitching has put them in big holes, with Sale and Porcello being the biggest underachievers on the staff so far.