It doesn't matter how poorly you force an opponent to shoot; if you keep letting them get offensive boards, they're going to score on you eventually. The only way to turn a missed shot into a stop is to grab a defensive rebound, and a player who can do that is just as vital to a defense as a player who can get inside an opposing scorer's nightmares. Xavier was an elite defensive rebounding team last season, grabbing almost 73% of their opponents' misses, good for 35th in the country.
What did we lose?
Dee didn't really do much on the defensive glass. His DReb% of 7.7% was about mediocre for a point guard, which is not a position you're counting on for the bulk of your rebounding.
Matt Stainbrook, on the other hand, was an elite defensive rebounder. His DReb% of 22.2% was easily in the top 100 in the country, and the amount of real estate he carved out for his teammates to go get boards opened things up for the team as a whole.
Can we replace it?
Matt Stainbrook was a great defensive rebounder, but he wasn't even the best one on his team. That honor goes to James Farr, whose DReb% of 30.5% is almost comical. Jalen Reynolds was also incredible on the glass with a DReb% of 24.6%. Both of those guys will be back and both figure to be once again capable of doing good work when the ball comes off the rim.
The only question really is how long those guys can stay on the floor. Matt Stainbrook was an offensive force and mostly avoided foul trouble, so you could leave him out there for long stretches without hurting the team in any facet of play. Since it seems unlikely that James Farr is going to suddenly become an efficient scoring machine, it would really behoove Xavier for Jalen Reynolds to become less foul prone.