He's a small part of the books. If I recall correctly, he molests Theon or some other kid in the books in a flashback.
I agree with everything you've said here. NK, it was like wow, but plausible.
Crossbows at long range?
Tyrion hiding in the crypts, that are full of dead people?
Messandei being captured after going belowdecks on a ship that sunk
The best military minds of the north running their entire cavalry blindly into the walkers?
Ghost surviving the cavalry charge
Just lazy writing or rushing or whatever. What's next, it's all a dream in a Giant's eye?