I don't know how it is with light novels but I remember reading that editors are responsible for like 50% of the final content in a manga, more or less depending on the prestige of the mangaka. I honestly think that probably accounts for some of the more formulaic elements we see repeated so often. The try to emulate what's popular instead of trying to understand why something is popular.
Awhile back, at the end of a manga I was reading, the mangaka published some of her rejected designs for the main character. Shockingly, the one that got approved was more attractive than the original and had the biggest boobs. I think that tells us a lot.
Mermaid Drive: Valkyrie or whatever was pretty bad. The art is kind of ugly and the Eiken-type breasts are strange looking. The masochist weapon-girl was awesome, though, and those have to be the most polite snakes on earth. Maybe this was the Real Snake Island? If so, they're lucky they didn't get bitten.
