That's true but using a 5 does show which schools are getting more to that higher level and which aren't. It might not be the right standard to measure schools against and it might not raise standards in itself, but it does provide factual information for parents. Looking at both the L4 and L5 and looking at those levels against prior attainment shows something about how successfully schools are moving students with those prior attainment levels on. It's still a blunt measure as these things always will be, but part of the purpose is information provision and there is increasingly more info provision.
For most people, rankings etc don't mean much because in reality they don't have much if any choice. Many will be able to choose between 1 or 2 secondaries. Bin my view, the more information available, the better, although I know people don't always access it or struggle to understand it.
I agree that if colleges etc are accepting 4s for the next level of study (surely not for A Levels though??) then that is a key measure....and to be fair, it is included in all the government tables. And okay 'fail' for half the population might not be helpful, but isn't any different to it was for the last 25 years with GCSEs when for practical purposes a D was a called a fail, even though all grades of G and above were officially passes.
Isn't it okay to say a 'standard pass' is good enough for progress to certain next levels of study and a 'good pass' is needed for others. Of course lots of places specify requirements above a 5 for some courses, which also must be okay surely? It can't be that anyone can progress to any course just because they choose. They do have to be suitable and have a decent chance of success at it or it's a waste of everyone's time and money. And those levels set for progress to the next level will also be a bit if a blunt instrument, but something is needed, so it seems reasonable to say a 4 or certain number of 4s gets you onto X courses, 5s are needed for y courses and 7s or above needed for Z courses. There also need to be courses for those with below 4s and they will have requirements too.
And I agree that simply saying a higher standard is now required doesn't magically make it happen. I can see that setting the standard first and then trying to make it happen is used because without the measure there might not be a strong enough incentive to really push towards that higher level, because the lower level will still be acceptable. Of course, before and as you set the higher standard, more resources are needed to achieve it....land isn't this where it's all wrong, becaue those resources simply are dwindling not increasing, so it is an impossible ask. Although it might not help the students achieving lower grades and their discouraged teachers, perhaps these consequences of underfunding in terms of performance need to be highlighted in tables etc - not to berate the schools, but so people see the failures of government to resource the education and standards they are requiring?