That's incorrect. Equal temperament is very recent. Medieval through Baroque used a system of temperaments called meantone that began with C major being in tun

That's incorrect. Equal temperament is very recent. Medieval through Baroque used a system of temperaments called meantone that began with C major being in tune, and then distorted tones slightly in order to make the proximal keys usable. Choosing a key in meantone implies a real difference in what the relative distance among notes was. When you go out beyond three sharps, it becomes very distorted. Five sharps is essentially unusable in meantone systems. Bach's well tempering was a replacement for meantone where all the keys were usable. We don't know exactly what it was, though there have been some interesting attempts at reconstructing it. I remember being in the orchestra for the Bach four harpsichord concerto as a demonstration of one such attempt, which was wild. As for using technology to create in-tune musical instruments, the original one, the voice, already has that. For keyboard instruments, there have been all kinds of crazy ones built over the centuries that have many more notes to an octave to allow much more precise intonation. But that's not the core restriction. I mentioned elsewhere in this thread that the pitch a given note maps to changes during a piece of music if you don't have tempered instruments involved, and those changes are always compromises. So I wouldn't suggest reading that discussion, as it's apparently full of inaccurate material.