I agree with most of the points you're making, but I do not think that the exams would need to be tailored to just the part of the curriculum that the students have actually covered.
If one student does not know key parts of the curriculum and the other does, then this should be reflected in the grade no matter what caused that difference, whether one of them got more schooling or studied on their own or took some out-of-school tutoring.
And if a diligent student who got all A's before missed out on key parts of the curriculum that's required for further study, then the final grade should reflect that they do not (yet) know the subject as expected and are going to need remedial support, i.e. their final grade should not be an A, the exam should ask for the expected content (no matter if it was not covered in school due to Covid) and the exam results and grade should illustrate whether the students have learned it otherwise or if there's a gap.
I'm inclined to agree, in principle, but this would mean that many students would end up with a lower grade than they could expect to have achieved normally. This would particularly apply to less-advantaged students whose schools and/or families have been less able to fill in the gap.
While that'd result in grades that would be far more meaningful than any of what's currently being done -- and universities, employers, etc would just have to take account of the special circumstances surrounding 2020 results when making admission/employment decisions -- I don't think it's politically tenable.
If one student does not know key parts of the curriculum and the other does, then this should be reflected in the grade no matter what caused that difference, whether one of them got more schooling or studied on their own or took some out-of-school tutoring.
And if a diligent student who got all A's before missed out on key parts of the curriculum that's required for further study, then the final grade should reflect that they do not (yet) know the subject as expected and are going to need remedial support, i.e. their final grade should not be an A, the exam should ask for the expected content (no matter if it was not covered in school due to Covid) and the exam results and grade should illustrate whether the students have learned it otherwise or if there's a gap.