Hey Remy... I talked to my buddy again. Basically he started with... It's always neat how 2 people can watch the same exact thing and come out with different takes on it.
He reiterated that Hollins was the deep threat that kept teams honest, even if he wasn't getting a ton of throws per game. Just running those deep routes would keep a CB and S occupied. When he went down, teams started playing more single high safety and stacking the box against an already weak run game. Switzer was the beneficiary of the constant WR bubble screens. Bug's tall, but he just didn't have the speed to stretch the field. He said the announcers even talked about how defenses were playing them differently.
Hollins averaged 24.8ypc in 2015 and his career average was a UNC record 20.6ypc. So he definitely was a deep threat target. That being said, since I didn't watch all the games, this is all second hand information to me. Take it how you will...
Hollins went out at Miami. Howard's previous game high prior to Miami was 69 yards. After Hollins went out, Howard had 156 yards against Miami, 109 yards against Virginia, and 120 yards against Georgia Tech. So Howard just became a bigger focal point of the offense so they adjusted fine.
The reason UNC's offense struggled a bit is because teams started game planning more against Switzer to take away Trubisky's favorite weapon. Switzer had like 101 yards against JMU, 208 yards against Pitt and 158 against FSU. Then there was the VT game which I will ignore as it was a hurricane but beginning with the Miami game (last game Hollins played), teams started focusing more on Switzer because he had obviously emerged as UNC's biggest threat. He emerged because his skill set matched perfectly with Trubisky's best trait. Switzer was wasted a bit with Williams because Switzer is a YAC guy and Williams wasn't the most accurate. He excelled under Trubisky because Trubisky could throw to him in stride underneath and he would just rack up the YAC. At one point he was leading all of college football in YAC. So think about how Brady uses Welker or Edelman.
Teams had come into the year worried about UNC's deep ball because of Howard and Hollins. Hollins averaged over 20 YPC but Howard also came into the season having averaged 16.8 the previous year. They were both deep ball threats. The difference was Hollins had more speed so he would typically be capable of getting more YAC after catching a pass while Howard was more of the deep ball guy that would catch the back shoulder pass which doesn't lend itself to a lot of YAC. But Howard was still a deep ball guy. As time progressed and teams got more tape on how Trubiksy ran that offense, they started to realize that Trubisky really loved throwing to Switzer and Proehl and having them rack up the YAC. So they tried to protect against the short stuff more hence why Switzer didn't have another 100 yard game until Stanford.
So it wasn't that UNC didn't adjust after losing Hollins. It was more teams started understanding how Trubisky was attacking them and they tried to take away the underneath stuff with varying degrees of success. However, it's not like the coaching staff could do something to adjust to that because the only deep ball threat they had was Howard and he did in fact increase his production as Trubisky targeted him more after Hollins injury.
Also the run game wasn't weak at all. Hood averaged 5.9 per rush and Logan averaged 5.4. The problem with the run game is that they didn't run enough not that it was weak. They didn't run enough because Trubisky liked to throw. He has the power to run checks at the line and he loved to pass. He was always looking to throw when he scrambled which makes him a better pro prospect while Williams would run in those situations hence why Williams had over 900 yards rushing while Trubisky had around 300 despite Trubisky being just as fast as Williams. So Trubiksy and the coaches just fell in love with his arm and that made UNC less balanced. But 5.9 per rush and 5.4 per rush is not weak at all.