What you just wrote is fine, but in no way does that mean we need 5CBs. I’d remind you your last line is exactly where we were last year when we had an excellent defensive record, including 3 clean sheets to finish the season when Romero was injured. If we sign 2 new top notch CBs and have Sanchez Dier and Davies as reserves that’s probably the best set of options in the league. It’s ridiculous to suggest we need or are going to buy a complete set of reserves on top and have Dier and Davies as our 7th and 8th choice options. Nor even chelsea keep that much squad flab aroundIsn't that the issue though? There probably isn't a better 6th choice combo than Dier/Davies in the division. The problem is that they aren't our 6th choice, they're our 1st and 2nd choice. I'd be perfectly happy with them as general injury cover, but with rotation even a second choice player starts one in three matches.
I haven't heard any noises of us trying to keep Lenglet, so realistically before we buy anyone in the summer our absolute 1st choice CB and LCB is Dier and Davies. We will be one Romero injury/suspension away from a back line of Sanchez - Dier - Davies to start the season.
The other positions I did say were arguable.