As a full-back, perhaps.
As a wing-back Chilwell did really well prior to the injury last season, though. He got 3 goals and an assist in 6 matches at the start of last season. Probably not sustainable numbers but Cucurella got 1 goal and 1 assist over the course of the whole season, by comparison. I like Cucurella and don't necessarily think numbers are the main measure of a good full-back/wing-back, but in Chelsea's system it's important they chip in because their forwards aren't particularly great in that regard.
Chelsea fans and Tuchel clearly rate Chilwell though, it's not as though they're signing Cucurella with a view to replace him.
Doesn't really bother me, of course, but it feels like they're just scrambling around trying to get any defender in after missing out on other targets.