^^ That's a huge risk to take... You'd need all 3 of those new starters to hit their top end potential for that team to be competitive. It's just not likely.
I don't see it as risk exactly:
Pritchard replaces Kemba
Markkanen replaces Theis
RWilliams replaces Thompson
Williams is already playing equal to or better than Thompson and this should only continue in that direction and be a net plus over time. Markkanen has a well established track record of way more production than Theis and this should be a big net plus over time.
The downside is losing Kemba from the equation but that is complicated due to age and injury concerns. This is really more about Markkanen replacing Kemba. Markkanen's current production is pretty close to what we are currently getting from Kemba and to me, getting this production from a big over a small is better in a meaningful way in terms of roster balance.
Realistically, if this team started to make noise and either Pritchard or RWilliams were not up to it, that could be addressed by a trade or signing. The key to this is trading the commitment to Kemba for a commitment to Markkanen. If he fails, we are in trouble but no more so than if Kemba tweaks his knee in the next game or just in general stays at his current level. We are transferring the principle risk from an aging, injured, declining, undersized guard to a highly skilled, young, full-sized big. To me, that is a major step in the right direction with still some risk but more strategic risk and more upside.