What do mangaka have against writing black-haired girls who are just, you know, normal?
You mean plain? Well, for this particular manga, every character has some sort of quirk/"disorder", including the other black-haired characters (plenty of them, and I don't think Tadano is normal either). "Normal" black-haired characters aren't actually interesting unless you're looking for a self-insert.
The synopsis for this story reads like it retroactively became the template for every lazy, boring, trope-filled romantic drama manga ever created.
I agree that the synopsis isn't very good, but at least it doesn't spoil anything;
a lot of things happen. The manga really does play on tropes, even subverting them a little (e.g. Najimi). If you're looking for some super-unique plot for a manga with a "Slice of Life" tag, then this isn't for you.
Read a few random chapters and yep, this is exactly as moronic as I expected it to be.
That doesn't give it justice. All the other characters (including male ones) are just as adorable as the protagonists. It's not even a romantic drama... or maybe comedy manga isn't really your thing? Then again, there
are so many characters, so you'd have to be pretty invested in the series already to like any of it.