I did my reading and fail to see how this is an issue with appropriate quarantine/medication which is just basic practice (or should be, anyway).
I have/had 7+ Discus and 4 angels (down to 2 - the other pair went back to work) together for months with only minor issues. Altums that were terribly skinny when I got them put on weight after worming treatments. I don't even think the altums and discus knew each other existed. They didn't mingle, fuss or fight at all. Now my small pair of Angels will have all my Discus up the other end of the tank when they are in breeding mode and they're half the size of my 'boss/dominant/biggest' Discus. If I didn't have a breeding pair, it would not be a problem at all.
Discus are more passive, slower moving, calmer fish. When I had a group of Angels, they were constantly in each others faces reminding each other who was boss, etc but never really challenged the Discus as they would hold their own ground very, very easily being much larger. Discus prefer to graze off the bottom while the Angels prefer to eat from the surface so my easy fix is feeding a pellet that both sinks and floats through an auto feeder set to go off four times a day with two rotations and regularly give them a huge amount of bloodworms so everybody can graze for 5-10 minutes and nobody misses out. Yep, they're all FAT as hell. Now if I could just find something to stop my Angel pair breeding, it would be paradise in there all the time...