just to add my two pence to the whole discus debate
firstly you are quite right, there is conflicting info on this forum, and sometimes people get things wrong. But that's what makes this forum such a great source of information. No one person knows everything about every species of fish, so if you look on a website compiled by 1 person there will inevitably be inaccuracies, take it as gospel and you could be in for trouble. On this forum individually we don't know everything, but when you combine our knowledge and experience we've got most bases covered and you should be able to get a good response to any question. Yes you may well get conflicting info on a post, but usually once a few people have replied you can see what the general consensus is, most of the time when someone disagree's with someone else's answer they will give reason's for it. Obviously occasionally there will be someone who spouts out a load of rubbish, but then the people who know what they're doing follow them round correcting it until they get the idea!!
So no, don't believe every word you hear on this forum, look for the consensus or if you aren't sure then ask people to expand on their reasons for saying something, when people have to explain things you'll usually see weather what they say is based on fact or just somethng they heard down the pub.
This applies especially so to Discus, when Discus were first introduced to the hobby they were virtually impossible to keep alive, they were really regarded as suitable for expert keepers only and extreme measurs had to be taken to keep them alive. Over time our knowledge of them grew and the tank bred strains becaome stronger and more tolerant of tank conditions, discus keeping is moving on, but advice tends to stick around for a long time. So you get a range of opinions from 'no you can't keep discus without loads of expensive equipment and space' to 'discus are actually fairly hardy and don't need thta much extra treatment' and everything in between. Really there is no overall consensus at the moment on what is best for these lovely fish so you will get a conflict of opinions, sorry this isn't much help to you but perhaps it explains a little of why you're getting confused. You just have to read as much as you can and try to make an educated decision from there. But with Discus don't expect some magic wand formula that someone's gonna give you which will make it all work perfectly straight away.
Not lets disect this slime coat theory, firstly what is slime coat, this is a natural protective mucus that all fish produce, it acts as a little barrier around the skin and will stop some irritants in the water getting to them. Sort of like having a big plaster all over you!! Now slime coat is a good thing for fish to have, if it gets removed they can produce more, but sometimes they can't produce enough of it quickly enough to avoid any issues. It's certainly not something you should be looking to remove from the fish on purpose.
So why would you want to add a fish which will remove it? Plecs also have sort of teethy raspy bits in their mouths and as we have established, discus are not the absolute hardiest fish ever, can you imagine the stress caused to a slightly shy nervous fish by having a great big plec clamping onto their sides and rasping away at them?!?!
Now I have heard of some species of plec and loaches sucking onto fish like this, never specifically heard of the association between plecs and discus, but lets assume that it is true. In what way can this possibly be a good thing and something you should encourage?!