It doesn't even need to be that fancy. Basic ones will just react to reduced flow on the hot or cold side by reducing the other side proportionally to keep the temperature roughly the same.

Ah, called a thermostatic valve here I think? Maybe?

The fuck?

This exist?

Did I live under the bottom of a well or something?

That's a thermostat and won't do you any good if the plumbing is set up in such a way, that all outlets are connected in series. You need a parallel approach (manifold with large diameter branching off to all outlets).

Those have been standard for a while now.

…and that there was no planned access to for replacement.

Not just the states….im in a (rented) house in Germany that was built in the 90s (so not that old to compare to a lot of other houses here) and deal with this everyday. Coupled with the insanely long cleaning times and frequency of use due to how small they are for the “economic” washing machines and dishwashers, fluctuating water pressure and water temps are always a surprise….

Is it like that? I remember this being an issue in the 1970s. Even crappy old places that I lived in as a student had balancers. I think they've been required here since the...90s?