Yes Ranger, I agree that it's just a hobby, they are only fish, and there's more to life - but they are expensive fish and I believe that most people who keep them want them to be healthy & thriving, so its only sensible for them to learn how to keep them that way. Discus do need more care & attention to water quality & conditions than most tropicals do, so discus-keepers must be prepared to accept the challenge that passive, laissez-faire, or negligent care will be insufficient to succeed at keeping them. I would hope you would agree with that.
Now on to the matter of how to tell healthy, well-shaped discus from those that are not well-conditioned and inferior.
As a whole, that is something that is more or less learned only after years of experience with discus, and observation of both quality fish, and non-quality fish, and runs the gamut from determining good or poor shape, good or poor coloration, odd or natural behaviors/mien, finnage, eye to body ratios, and other factors.
On top of that, it's much more difficult to gauge those factors from looking at photos, than by actually observing the fish in the flesh, and at close range.
In the case of your fish - I can tell you this - by looking at the second photo above, the two small blues on the left side do appear to be (and I'd bet on it) no more than 3" in size from nose to tail base, perhaps less. Their fins are not fully/well outstretched, the eye to body ratio is not good, and the stress bars on one are dead giveaways that the fish are not in prime condition, and likely stressed from poor water quality & conditions. Furthermore, since they are likely more than 18 months old (even if were less than 12 months), with good care and attention they should be twice that size. So my conclusion is that they are stunted ( again, due to poor water quality).
The orange and red fish to the blues' immediate right are not much bigger, and they too don't look to be in anywhere near prime condition, even though the head- on shots are not a clear indicator. The pigeon-based fish on the right side is larger but the slightly clamped fins are an indicator of stress, as is the uneven coloration.
Your substrate is bad news - it's contrary to what you think - the larger size gravel would actually trap & harbor more undesirable matter. What you want is, imo & e, the best discus substrate - and that is nothing more than #20 grade density inert quartz-based silica pool filter sand - which is easy to keep squeaky clean at all times.
Artificial plants too, are notorious detritus gatherers only, having no use for any nutritional value from organic waste material.
You say the background is fully epoxy sealed, but is it certain there has been no leakage, and that there is only air behind it - no water and no waste matter ? I have seen a number that were considered sealed at inception but didn't remain that way for very long.
If I were you, I would rid the tank of the background (put something else on the outside of the tank), use PFS as substrate, along with a limited number of live plants (or no plants at all - perhaps just driftwood), and do large (50% or more) water changes at least every 2nd day, at which time I would vac the substrate well, and do a thorough tank glass wall wipe-down with each & every wc.
And I would get discus of not less than 4 " in size (preferably larger) from a well-known reputable supplier of quality fish. In your case, quite frankly, I know of no discus providers of top quality in Washington state (including Macs who I have knowledge of). Your best bet would be deal with Kenny Cheung, of Kenny's Discus in Daly City, Ca. (near S.F.) who will air ship & guarantee live delivery of high quality, well-shaped discus.
Btw, will you explain your automated water change system in broad terms, so I can understand how your wcs are being accomplished.
I'm willing to assist you with anything more that you'd like some feedback on, and I wish you all the best with your discus-keeping.
