it depends what the purpose of grading is. if the people is to purely assess, grading question by question is better. if the purpose is to provide feedback, knowing how the student did in general can substantially help with identifying what to emphasize
The reddit explanation in the post addresses your question I believe. If someone is at a 28 or 29 a few "charity" points can be found in subjectively-graded tests.
I think that really just reflects the fact that on subjectively graded tests the score really doesn’t have that many significant figures of accuracy. That a regrading can find 3 to 5 points by being more generous - or presumably take 3 to 5 off by being harsher - says that really you could save a lot of effort by treating the final grades as bucketing into 10 point bands and treating 25-35 as the actual cutoff.
Unfortunately this is the final exam from pre-university education. You can think of it as one's first educational degree, a step below bachelor's. It's expected - particularly by employers - that everyone should achieve it.