What output is higher...?

My friend has Oracle Alexandria with Grado ZF3 cartridge/Prelude tonearm. I assume that ZF3 is MM cartridge and must have at least 3mV output. Input sencitivity of the phono preamp Michell ISO is 0.9mV.
When I connected my reserve Benz M.09 to his arm and than to the phono preamp it sounded much louder on the same volume levels of preamplifier(Monolithic).
Listening to his setup with ZF3 I realized that there is not enough gain in the system giving a mushy dull and shallow sound but I couldn't understand why... Can the output voltage decrease within the age of a cartridge(7y.o)?
Or can I assume that the cartridge sustained a damage and needs a re-placement...?