The real answer is to make off the shelf audio gear bulletproof to these factors; but this will take some research, and commitment to proper engineering ...
You make some good points. This last one is of particular interest. You're right and wrong. IMO.
The problems causing by far the greatest levels of distortion lie within the equipment. For example, John Curl said a few years back that all of his designs (and everybody else's too) contained at least one serious and unknown flaw.
He and I kinda' got into it but I tried to share with him that these were not flaws at all. I tried to explain that the components were simply incomplete in their design. And there's at least one most significant aspect that is outside of the designer's scope and control, though they could certainly improve on some aspects. The less but still significant flaw of conditioning noisy AC could perhaps be addressed within the component, but I'm not aware of any designer who has successfully and superiorly accomplished this yet. To the best of my knowledge, it's been accomplished by only a few mfg'ers of external line conditioners.
But that's ok. All one need to do is sift thru the haystack for a rare but superior line conditioner (most aren't worth owning), and noisy AC problem solved or at least greatly minimized. But with regard to noisy AC, most still don't believe in it. Most likely because their only experience with line conditioning, if any, was probaby with an inferior line conditioner that actually induced its own noise making the presentation sound even worse. The only problem there is that the enthusiast thinks all line conditioners are the same, and since his system sounds better without a line conditioner, his equipment must have been superiorly designed such that it doesn't need any AC filtering / line conditioning.
I mention this because it's actually a huge problem and obstacle. And designers face the exact same dilemma and thoughts many times. IOW, if their designs sound better without line conditioners (an inferior line conditioner), then they too are convinced there is no problem with the noisy AC from the street that universally impacts every last enthusiast. At least in the USA.
Hence, they (designers) don't see the need to do anything about it. And here we all are. As usual.