I don't know why this has to be explained a million times but this is going to be the case for pretty much any team dealing with [multiple] injuries. You can't get rotational quality players to come sign for lowball NIL and be expected to play zero minutes the whole season in the case that there are minimal injuries.
Duke went to a 6 man rotation when they had guys injured
Texas Tech went to a 6/7 man rotation when Toppin went down
Michigan went to a 7 man rotation with Tschetter playing spot minutes after the Cason injury
UConn was playing 7 guys when they had injuries
Iowa St played 7 after Jefferson got injured
Alabama played 7 after Holloway was arrested
Gonzaga played 7 after Braden Huff was injured
That's why you're not going after a 9th man. You go after a guard that pushes Coleman for a starting spot or is the first guard off the bench if Coleman is better.
You bring a guy in with the intention of them competing, not being a 9th man. If Morillo and the other freshman are better than great, if not you push Morillo/Davis down the rotation to where they are better suited and you're not so reliant on them.
As far as the teams you're pointing out I don't think they are making the point you want to. Michigan was 9 deep all year and played 8 deep without issue when Cason went down(Tschetter was absolutely past of the rotation playing 10-15 mins). UConn was 9 deep all year and dropped to 7 when Ball and Demary were hurt before being back to 9.
Those were the only two teams that were able to weather the storm with injuries.
Duke was 8 deep and Siena had them on the ropes with 2 guys injured while they had two former top 50 recruits(Harris(so) and Wilkins) that couldn't get any tick when they desperately needed help.
Texas Tech, Iowa State, Alabama, and Gonzaga were all different levels of cooked as soon as they faced injuries/depth concerns. None were really title contender at that point.
Illinois is going in basically counting on Coleman and Morillo to be 8 deep with the 5 returnees and Vaaks. If none of the other lower rated freshman are ready to play than that is it(More likely than not). If one of Morillo or Coleman doesn't translate right away then you're all of a sudden trying to play the season 7 deep with Davis as your last guy - someone goes down and you look like the Wisconsin game real quick.
It's basketball, an injury can always kill a season at anytime but if you have the money why not get a guy to compete with Coleman and buy the freshman time to come along at their own pace. Just because Brad has struggled to manage rotations(see Morez minutes) does not mean you cant play 9 or even 10 guys in the regular season and condense down to your best 7/8 when you need it.