It seems there has been a battle of the fish masters in here (just kidding).
Anyways...Well, about the crypto vs lympho... well you could definetely have both. And from what i can gather, lympho has no real treatment, so diagnosing it just tells you that you can do nothing. BUT, it also looks like you have crypto, so start treatment for that. WIth any of the diagnosis', treating for crypto would be a good option.
Though, if all of that is cryptocaryon, then you might want to remove all the fish into seperate tanks that are removed from the display. Who knows how many encysted crypto there are in all your tank's nooks and crannies. Every fish is at risk of being infected (if they arent already).
And about the fish acting normal, they either numb to the parasites or maybe they somehow "got used to it". Maybe they adjusted to throw off just the right amount of mucus at the right times to prevent a lethal infestation. When a fosh gets ich, it starts mucusing like mad, but mucus doesnt come out of thin-air, i mean, thin-water. It takes energy to do anything, including making a mucus coat. So maybe SOME of the reason why a fish gets really dreary and tired and lathargic w/ an infestation is that is has gone through its energy reserves. You said you feed him a good variety of food, vitamins, antibiotics, etc., well maybe you're successfully stopping any secondary infections while keeping up the fish's energy.
NOTE: These are just ideas that i said in order to get "out of the box". I know its not all necessarily likely, but it seems possible to me. You dont have to agree with all of it, but if it helps in any sort of way, im happy. Plus, ive been watching a whole lot of "House" recently, every symptom counts.