Would be a good argument... except 1% x 1% isn’t 0.0001%.
Things such as asthma can cause an OML, which when flying with a clean pilot, is fine. You would like both pilots to be able to have an OML, what if they both had asthma? What if there was a fumes event? The rule is there so that if an aggravating factor caused incapacitation of one pilot, at the very least it shouldn’t incapacitate the other. To allow it would mean scheduling people with an OML of X variety to only fly with an OML of Y variety and it would be very messy, as I’m sure you can appreciate.
That’s ignoring the fact that I’d be surprised if there were many people happy to fly if they knew both of their pilots had heart conditions requiring an OML restriction, for example.
I also don’t quite buy the age discrimination argument. Pilots aren’t being discriminated against because of their age, they are being discriminated against (rightly or wrongly) because of their OML. It just so happens that as we age we are more likely to have conditions that would limit our medical, up to the point where at 65 it’s game over for flying (for now - hopefully AUS can change that). The fact that there is natural process of ageing is just life I’m afraid.