I wasn't aware that either threaded retainer needs to be all that tight with a cartridge bearing BB. I have some IRD French and Italian (and Swiss) threaded/splined retainers (sold as accessories) that are aluminum, though I haven't installed a BB with them yet. And the NDS retainer on many budget-level Shimano cartridge units is plastic, for Pete's sake! I only have one cartridge bearing BB installed, with steel retainers, but it's been fine for years, and I don't remember installing it really tight (like tight enough to use a torque wrench) -- in fact I think that the instructions even warned against over-tightening.
Of course if an existing unit has been installed using the overkill method, ya' gotta remove it!