While I agree with the sentiment here, but it also confuses me. You say we knew how it played months ago, but at the same time, you say that playing the beta's not a fair way to assess the game. What, media reports from before the beta are fair information, but personal experiences in a nearly-finished demo aren't? I guess I'm just confused about how you seem to be saying something that contradicts your previous stance a bit.
Ehh, I think ratings are too generous as a whole. For example, you call 75 average, but I think it to be a high rating. I have always stood by the idea that using a 0-100 scale, but calling anything under 60 worthless is dumb, because you're literally wasting more than half of the scale--in which case, why have it? I'm one to say that an average game should be sitting at 50, not 75. My short time with Destiny would put it at about 60, which would be a bit north of average, but nothing great.
So, while you say 0-4 ratings are throwaways, I would say that 4 is a valid rating. If you're a big story-driven player, and you agree with the general idea that Destiny does a poor job delivering a mediocre story, a 4/10 could be a fair assessment. You might not build your opinions on mechanics as much as atmosphere/experience, so the negatives of the game might stick out more, in this game's instance. It's almost the inverse of how people can praise Dark Souls, even while calling its controls shoddy.