CheesyMacgyverthe only situation your medic can pick up the enemy medics ubergun is a situation where you will have uber advantage either way you just get uber faster now which speeds the game up (less time for lvl 3 gun and heavy) more ubers more fighting
except if you drop an uber
or if both medics die you can pick up a medic's previous ubergun
or when you're pushing into an uber advantage you can target the medic and then possibly pick up that uber and now you have an even bigger advantage