people get caught up in the hype

Utterly undeniable, but I think it's something small compared to the other issues below.

people rate far harsher with shows they don't like (which is why even good moe shows will have their ratings demolished

I guess that explains the apparent anomaly of Hibike's rating compared with its popularity on this sub, which I chose to ignore as I haven't seen it so I have no useful input to make there.

sequel bias - ratings are either higher than usual due to those who liked the show watching the sequel (and not those who didnt) or swing heavily due to changes to formula

Which is why Zoku is doing so well in the ratings whereas Nisekoi: is not. Zoku has been well-received both in terms of a sequel and in its own right, whereas Nisekoi: has gone down from series one and is in the middle-rated group of this season's shows, despite having weeded out some of the people who didn't like S1.

And I think that's totally fair; Nisekoi: is both a bad sequel because it feels on the whole more episodic patently in order to delay the progression of the plot unnecessarily, and a bad series generally speaking because the characters rarely interact with anyone other than Raku, leading them to be largely undeveloped, and yet still even more characters are being added into the ring (Haru) to compensate for the fact that its existing characters are already vastly underdeveloped.

Mainstream shows and those easier to consume are shared among a wide range of people ... aala NGNL, KLK)

And why were they so popular? Because they're exceedingly good for what they are. ^{Obviously speaking from a biased perspective, but I think it's absolutely criminal that Kill la Kill isn't in the top 200, considering the junk that's in there.}

Same with OreMono: why is it so popular? Because it's a fantastic cute romcom in a medium where (a) a large quantity of romcoms are harems and (b) the ones that aren't are dismissed because they're shoujo and a considerable proportion of anime fans don't like it because it's not intended to appeal to their demographic. If anything, I'd say the post-release anti-hype makes the ratings more inaccurate for judging show quality.

Lastly,

You made some other great points, which I won't address for fear of boring you, but on the whole I stand by what I said, that on the whole MAL scores are better indicators for airing anime than for completed ones. I'm not saying they're perfect but I still think they're better than MAL scores for anime generally.

I think this might actually be a very good idea for a separate thread later down the line.

If you're serious, I'd be more than happy to leave the potential posting and credit of said thread to you as I think you've probably done more of the "work" here (and, it has to be said, your popularity is certainly useful for preventing discussion threads from turning to shit) but if you do decide to post an analysis-come-speculation-come-discussion thread on the subject, I'd be happy to write an agenda/outline of my standpoint in order to make the discussion as unbiased and debate-provoking as it needs to be.