That isn't what the parent said. If the highest rating is set such that vehicles that achieve it demonstrate a high level of safety, it would then be preferable if all vehicle makers strived for this rating. Assuming you want to drive a safe vehicle, it would then also be preferable if this rating was also the most common since that would indicate that most vehicle makers are building vehicles with a high level of safety.
Actually it is what was being said, unless there is some horrible misunderstanding that achieving the highest rating in tests like this indicates that automobiles require no further safety improvements.
wfme expressed my sentiment well. I don't really know, but if, as you are implying, these tests aren't an assurance of safety, than that point stands even more!
They aren't exactly an assurance of safety but such tests should simulate a number of the most common and most dangerous types of crashes and score those. This test comes from the insurance industry so we should expect they are motivated to prioritize according to the risk of damages payouts, but hopefully that should be a decent proxy for safety in any case. So better results should generally mean safer.
I'm not saying the tests are not good. But the value of the results is informing consumers about the safest cars which then encourages industry to compete on safety. If half new cars get the best ratings then that means the test no longer motivates the industry to improve the state of the art in safety and it's just about pressuring the trailing products to catch up.
So for example if your argument is that automobile safety is now at a point where it doesn't make much sense to improve any further then this would be fine. I wondered if that was your reasoning.