I would disagree that Chilwell and Thiago Silva do not improve us defensively, but I cab accept the fact that people have doubts about them. For what it's worth, Chelsea have also hired a guy who I'm told is going to be the nee defensive coach, so perhaps some of teb structural defenaive issues will be addressed.
Having Kante back fully fit will also help in that regard, but I think the biggest plus is going to be having a new keeper between the sticks, and I'm fairly certain we won't go into the season with Kepa still first choice.