That's not how survivability calculations work. It's calculated by comparing tanks lost to tank crew casualties. Like how cars are absolutely safer today since automobile fatalities have remained more or less unchaged fir the past 50 years despite the number of cars and drivers on the roads tripling in that time. Every man had his own escape hatch, and the tanks were purpose built for reliability and safety. You couldn't just take a tank from Normandy and put it on a liberty ship back to Detroit to get it serviced. They had to be robust and easy to maintain in the field, while keeeping the expirienced crew safe, since a seasoned tank crew is worth more than 10 tanks with no one to operate them.

German panzers had high kill rates for two reasons: they were on the defensive by the time the Sherman made it's way to Europe, so panzers got to initiate most encounters, giving them a massive advantage, and the kill rates mostly come from the Germans, who lied through their teeth anout how many Allied planes and tanks they destroyed throughout the war for propaganda purposes. And how can you verify the tank commander's claim of three enemy tanks destroyed with all crew eliminated when the site is now behind enemy lines? And why would Goebbles even care to verify when he could use those preposterous claims to claim the German war effort was doing just fine?

To be fair, it was a pretty well designed tank and crew survivability as well as ergonomics was a big factor, meaning Sherman crews had a pretty good rate of survival (the implementation of wet ammo storage is also a big one for that)