I honestly don't think exams are a good way of measuring performance at all. Like in no way. I get the reasoning for them but it's also just not a useful metric.
For example, maybe this is a "too woke" take but I think exam periods are sexist because people who menstruate are almost certain to be on their period during exams. Endometriosis affects MANY afab people and can lead to difficulty focusing as a result of pain alongside other symptoms which amab people won't have. People can get sick (which is more common in poorer areas and those people are less likely to be able to afford proper treatment). People may have other life circumstances or mental health issues which can impair their ability to take the test. And that's just the problems of having singular exams determine grades, not to mention the nature of exams.
People with disabilities can get additional access arrangements (which I have) but not everyone will have those diagnosed or be aware they need it. Someone may be dyslexic but they have A Method so they perform well enough in class but struggle when it comes to the exam. Someone may have OCD that means they take longer but they still pass so it isn't flagged as an issue.
Even then, exams are unrealistic. Sure being able to recall knowledge proves you know it and that's important but in reality you will pretty much always have access to books or the internet or COLLABORATION WITH OTHER PEOPLE to solve problems. I honestly don't think memorising quotations for literature subjects is useful in any capacity. And again, all of these "exam skills" are significantly more difficult for certain people. Mental health issues can lead to memory issues and difficulty focusing which is unlikely to flag up as an issue (but even if it did many schools are awful at helping students with that sort of thing because education is largely underfunded).
And that actually segues into another point that the quality of your education is determined by your environment. I'm lucky enough to go to a grammar school and have always had a good teacher for a subject but not everyone gets that privilege. Private schools have significantly higher scores overall but are blocked by a paywall. Even scholarships can lead to social isolation compared to peers who have a lot more money. And of course there are people working jobs to get by who don't have as much time for revision.
Then with the actual content on exams, compared to the mass which is taught, there is hardly ANYTHING. Entire topics won't come up so if you lucked out and something you're good at is on the test, good for you. If you happen to have one topic you excell at and that makes up the majority of the paper, it doesn't prove that you're good at a subject. And in the same vein, if you only get topics that you missed due to illness or that you struggled with, your score will reflect that even if you got perfect scores in every other one. It's random and doesn't adequately display capability.
The education system (at least in the UK which is the perspective I'm writing this from) has lots of flaws but limited examinations only exacerbate them.
I don't know what exactly the better alternative is but general coursework counting towards final grades is a much better alternative. I believe that's similar to how high school works in the USA but I'm not certain.
