Most toilets in the US are created to be "green" when it comes to water usage, but the reality is it takes at least 2+ flushes most of the time instead of 1 because of it - but as long as the amount of water per flush is low it passes regulation.

In my experience, the US toilets from ~2000 to ~2005 were crap (heh), but since then they've figured out how to make a low flow toilet that works, and it's fine.

Or if they are Trump 10-15 times: https://www.youtube.com/watch?v=VygBCFQVFgM

Low flow toilets are the worst.

A good, modern low flow works better than the old high flow toilets. A few years ago I lived in a new house with a Toto low flow. It was the best toilet I've ever used.

They used to be pretty bad, but with time I think they've gotten to be just fine.

You can't cheat physics. If you dump X gal of water from Y height it will have Z kinetic energy minus efficiency losses. We've greatly improved the efficiency of the water dumping mechanism over the years but a high end low flow toilet of today is still nothing compared to a high end toilet of decades past. That said, there's a lot of crappy old toilets out there that don't flush any better than a modern low flow toilet and take 5+gal to do it.

Source: Moved into a house that was once owned by wealthy people. The upstairs toilet was clearly top of the line circa 1940s and is awesome. The downstairs toilet was clearly subject to some serious compromises for packaging reasons and is nothing special.

You most certainly can improve upon bad implementations. Kohler's most recent line (within the last 10 years) are considerably better than all toilets I've had before. They consume much less, flush once and don't make an excessive amount of noise.