Light rail is horrible. Take a ride on the BART is SanFrancisco to see how it transports bums around the city. Super uncomfortable for commuters to endure the filth just outside (and often inside) the stations. Need to trip over the bums (homeless if you prefer) step around there feces and be careful to not step on their mass of discarded hypodermic needles
You can say the same thing about any kind of public transit.
A lot of that has to do with the problems that exist in a given city, and their transit authority. If you have a huge homeless problem and huge drug problem then of course they're going to spill over to public transit. Hence your comment about trying it in the US because obviously you know outside of the US the story is entirely different.
The most experience I have is with Portland Max system. Over the course of years I've seen times where it's really clean, and times where it seemed like the only purpose of it was to transport bums in loop. But, then they step up enforcement and its good again.
I don't think we can blame light rail for problems within the city.
As to buses being more efficient that's entirely incorrect. The problem is traffic, and the fact that what makes them easy/cheaper to implement is that they run over the same roads as other cars/trucks. That makes it an unreliable form of transportation.
Obviously autonomous buses/cars with their own dedicated roads would be idea, but I don't see happening anytime within the next 50 years.
Apparently the only thing we agree on is the need to ban cars from city centers. In places that have banned cars I can walk from point A to point B faster than it would have otherwise taken me by car. Assuming a radius of around 1 mile in a densely packed area.
We really need to rethink how people get around in city centers, and outskirts of the city. Things like ride shares, shared bikes, scooters, e-bikes are rapidly changing how people get around.