It's not overly surprising to be honest. A school like SU is going to struggle to have more then 2 capable QBs in the system maybe 3 if you have a very good walk on See Mahoney during Babers early years.
The problems are 2 fold for SU. The main issue is that Collins has been bad and at times unplayable. SU isn't Bama or Ohio State, if your back up QB isn't the answer 95% schools are gonna be in major trouble at this level. Similar to the NFL , very few teams have a capable backup much less a 3rd guy they can turn to.
The other issue is that the rest of the backups are all literally true or RS freshmen. SU doesn't have a Sr or Jr who hasn't been good enough to get a shot but has enough knowledge and experience that they can give even mediocre production out there. The choices behind Collins are 3 true freshmen one of whom is a walk on and the other is a Rs-Frosh who lost out on the third QB battle to one of the true freshman and has struggled mightily. Certainly fair to blame the staff and their QB evaluation abilities.
The schedule, a maddening inconsistent defense (ERob issues) and Frans uncertainty of what he wants to do has all played a role.
As frustrating as this is, it happens more then people think. Happened last year to FSU though the injury was later on, the horrific QB play ultimately imploded the team. DItto Kentucky. There was another team last year as well who was down to like their third or 4th qb at times and it was a disaster ( I can't recall who it was, I think a B12 team). Angeli was the one guy they could truly not afford to have get hurt and unfortunately he did.
They will have to try and get a better back up next year be it a recruit or a transfer or even a D1AA or D2 guy who wants the D1 experience and is OK playing behind Angeli.