Well, obviously you don't understand what 'loophole' means in this context. Let's go with your looking-at-houses example. You look at a house, then look at another house, and sure enough they are 50 ft apart. You do this a bunch of times, people come in and verify it, that's all well and good. As you said, it becomes accepted that the houses are 50 feet apart and that's good enough for you.
*But you didn't actually close any loopholes!* What if looking at the first house makes the second house move to its current location? You only see it at one point in time, maybe the houses are communicating to each other so that when you see one house in one spot, the other 'knows' where to be. Or, since you aren't the only one who ever looks at these houses, maybe the times you (and your collaborators) looked they were 50 ft apart, but the passersby, who you didn't ask, see them as 20 feet apart! Basically you just got lucky, every time.
Or, the mega-loophole, maybe when you see a house your brain is tricked into thinking that the next house is 50 feet away, that is to say that looking at this particular set of houses interferes with your freedom to choose your future actions. You can maybe see why it's literally impossible to close this loophole.
The way this works is that people see the houses (observe non-classical correlations), propose superpositions/quantum mechanics as a model for why this occurs, and then other people say AHA! but it could also be that there are other properties that we don't observe which make these things happen! Those are the loopholes, the things that make alternate theories possible. It is not in any way a basic problem with the measurement, its ability to predict, or to be verified.
Again, it is not possible, in any way whatsoever, that the 'experiment is measuring nothing'. It is possible that the experimental results can be explained by a non-QM theory ... unless you close the loopholes on which other theories rely. So now we're down to QM or theories where you lose freedom of choice.
This shit about 'light adding up to one' and how it's nonsense to 'use light to test reality' is complete gibberish. This experiment measured electrons btw, if that helps you sleep at night, and entanglement has been shown to exist with pretty much every natural quantum including photons, electrons, neutrons, protons, vibrational modes of crystals, you name it.
edit: Entanglement is in no way 'just a mathematical construct'. It describes why, if I take two photons prepared in a certain way, that if I measure their polarizations independently they agree, and also if I take one photon of the pair, flip it's polarization, and measure, the polarizations of the pair still match. It is impossible classically, where photons have a definite polarization at all times. QM puts a mathematical framework around this phenomenon and makes predictions, but the observation is as real as your houses. I don't know what more you want from a scientific theory.
