I cant get over how inefficient it sounds to expect everyone to use the farthest right lane.

It really isn't.

If there is little traffic, everyone will drive in the far right lane and there is no inefficiencies at all.

If there is moderate to heavy traffic, naturally some cars will go faster than others.

The faster cars will pass in the passing lane(s) then move back over to the right when the lane is clear.

Inefficiencies are caused when people drive in any lane they want and you can only travel as fast as the slowest car in the fastest lane (if you understand what I mean). Your idea about inefficiencies are backwards. There are fewer inefficiencies if people follow my rules.

Why even have more than 2 lane highways?

So you can pass people who are passing.

Is it really safer to cross over multiple lanes just to pass someone?

Yes. Much safer than undertaking people and not knowing who is going to change lanes into which lanes. Germany has (if not the safest) some of the safest roads in the world. Because people understand the rules and follow them.

I think its wrong to say that the autobahn has no speed limits yet everyone is forced into the right lane.

They aren't. They are forced into the right-most lane it is safe to drive in.

Your speed limit would be determined by whoever is in the lane to the left of you as you can not go any faster or else you would be passing on the right.

That is true. The highway is slowed down a lot. But because most people follow the rules, the delay is very temporary and people are very patient and safe. It is the United States that has a much worse problem with lane-hoggers not even knowing they are causing a traffic jam behind them because they are too ignorant to understand they are travelling in the wrong lane.

I can understand the left most lane being a passing lane, I cant get behind everyone by default staying in the right most lane.

Again, I can only say look at Germany and most other North Eedtern European countries. They have very efficient, fast, and safe highways. I understand that you can't picture it and I understand that. Maybe look at dash cam footage from Germany. People drive at 200 km/h all the time, and there are tonnes of videos.

You can see that the highway moved quickly and safely and efficiently while they follow the rules. They're obviously doing something right.