I'm afraid you are not correct. People trying to merge later causes more problems and actually leads to gridlock. People staying in the correct lane keeps traffic flowing and frees up the other lanes you insist on talking about for people who are going a different way. :-)

'Even if they used two lanes instead of one, that would cause a problem only a few metres down the road when two lanes becomes one at teh on-ramp.'

Yes it should cause traffic problems in roundabout beacuse of bad design. This is how it should be.

Car needs to use all possible lanes then tries to merge their goal lane towards to end. Not wait in leftmost lane of 6 lane road while all other lanes are empty. This is wrong.

Yes of course it's correct behaviour. Nothing else would work. Even if they used two lanes instead of one, that would cause a problem only a few metres down the road when two lanes becomes one at teh on-ramp. Traffic would grind to a halt on the roundabout, preventing cars at exit 4 entering teh roundabout and the whole thing falls apart :-)

So do you believe this is the correct behavious it should have??? Because I dont think so.

That is because they are all going left then left again. None of the vehicles being simulated in this picture has any reason to go anywhere other than the highway. if there was traffic heading to the residential district, it would use the other lanes :-)