Think of it in these terms you are a human, humans are closely related to apes, but would you be happy to be kept alone with a bunch of apes? Now genetically it might not be a perfect example but its in theory good. Humans can interact with apes but for total fulfillment most humans must be around and interact with other humans

Same with discus and other fish they are closely related but no substitute for another discus
Sorry, that is a poor analogy. The difference between humans and apes is a massive leap in intelligence, rather than ways in which socialisation takes place. Uaru and discus are right on a level, intelligence-wise, as well as socialising in very similar manner.
There is a lot of "internet" wisdom about uaru as well, that they MUST be kept in groups. However, if you dig a bit deeper then it appears that as the fish mature they become much happier with their own company, and that adult uaru kept as singletons pretty much always are very happy and settled.
There was a relatively recent thread on "Simply" about this very thing with discus and a number of people expressed an opinion, based on experience, that once discus get bigger than the juvie stage then they CAN be kept as singletons well, and be happy with it too. There was actually very little argument with that analysis either on that forum.
So people can repeat what they have heard others say all they want. However, if anyone has
actually kept a single discus before, then I take a lot of weight in what that person has to say. Experience speaks !
Of all the actual experiences of people who have actually kept a single discus in a community-type situation that I have read. Only one of these had a negative outcome, and ended up putting the fish with more discus, where it became much happier. All the others (remember this is other people's
actual experience) had great success, and their discus were happy, healthy, feeding and settled.
I will continue to search for these stories, as I'm sure I haven't found them all yet.
Now my experiment might fail, but if it does, it would appear to be counter to what I'm actually reading from people who have done similar to me.