3) The Rich Hill+Ji Man Choi trade hurt the Padres more than it helped
The big move the Padres made at the trade deadline was the deal that netted them Rich Hill and Ji Man Choi from the Pirates. The fact that this was the big move Preller made was disappointing as the Padres were nowhere near a postseason spot at the time of the deadline, so him being more aggressive of a buyer or selling some expiring contracts felt like the rational thing to do. This deal felt like a lame attempt at showing the fan base you were buying, but not really.
At 43 years old, Rich Hill had a 4.76 ERA in 22 starts with the Pirates this season. Expecting him to join his 13th team and somehow catch lightning in a bottle didn't make much sense, and he only made the team worse. The southpaw struggled mightily in five starts before being moved to the bullpen to finish the year. He pitched decently well out of the 'pen to lower his Padres ERA to 8.23. Nope, not a typo.
The Padres went just 2-8 in games he appeared in, and missed the playoffs by two games. Obviously the losses weren't only on him, but it's not unreasonable to claim that this team might've squeaked into the playoffs even if they stood pat instead of acquiring Rich Hill.
Ji Man Choi is a bit harder to blame, simply because he missed most of the stretch run due to injury. While that's certainly not ideal, he had just two hits in 31 at-bats with the Friars. Both of those hits came on the second-to-last day of the season after the team was eliminated. He was hitless in 24 at-bats while they were alive.
To sum up, Choi was worth -0.3 fWAR. Hill was worth -0.4 fWAR. You can realistically say these two hurt more than they helped, which is unfortunate considering how likable they are as players.