I agree with this post to an extent -- I do think the five returning players will help keep the defense solid -- but what you're missing here is the fact that there are going to be FIVE brand new players, including four true freshmen, plus the two players who redshirted last year (Johnson, Kiss) who have never played in the Big Ten. That's a lot of players to incorporate into playing defense the way Pike wants. I have to think there will be issues with TEAM defense because many of the guys are learning how to play Pike's defense.
The other part of "defense" is REBOUNDING. We lost our best front court rebounder (Freeman) and our two best backcourt rebounders (Sanders, Williams). I have to think that our defense will suffer because the rebounding percentages will probably take a step back this year.
I think Kiss and Johnson will have a leg up, as they've been part of practices and have been coached for a year within Pike's system with his expectations. Yes, they haven't done it at the B1G level yet - but Kiss has had Div-I experience before RU, too, so he's not as green as Johnson. Carter is also a Juco, so he has had more on-court experience than the freshmen coming in.
The potential defensive liabilities will be with the three true freshmen - Mathis, McConnell, and Harper. We've heard some good noises coming out of practice about Mathis' defense - but they'll have the biggest adjustment to make coming out of HS.
Looking at defense by position:
Guard - We lose Sanders and Williams, who were both upperclassmen and some of our stronger defenders on the perimeter. But we also no longer have to rely on Mensah and Dadika for about 8 min/game at the PG spot, either. Baker returns, and Kiss as a RS Soph with a year at RU under his belt, but we also add Mathis/McConnell as true freshman. I'd imagine we'll take a step back a bit defensively at the guard spots as the newcomers get up to speed. We have more length, but lose Sanders' footspeed to keep up with penetrating guards, too.
Wing - We lose Bullock/Williams. Bullock was a defensive liability, and Williams didn't play a ton at wing last year. I'd expect Thiam to continue to improve next year, and we'll see Harper and minutes from Kiss at this spot. Don't see a big fall off on defense here.
Bigs - We swap Freeman/Sa with Carter/Johnson, and bring back Omoruyi/Doucoure/Doorson. Losing Freeman is a double edged sword - he was a great rebounder, but struggled at times on defense against bigger bodies. Sa was a solid defender, too. Omoruyi was probably our best defender last year, and will likely be seeing more minutes. I'd expect Doucoure/Doorson to improve from last year, too, based on experience and health respectively. Remains to be seen what Carter/Johnson will bring, but I don't see a big step back on defense here. Maybe in rebounding - but Freeman's boards might get spread out across more positions than just the PF spot.