...
I could go on but do I need to? I know lore is lore for a reason but when the reward comes nowhere near matching it I become a little disappointed.
Ah...I see, I see. I admit, I was more than a little underwhelmed when I finally got my hands on the Razor, only to see that the insta-kill only pops 5% of the time "at best". I still use it sneaking or off hand with Molag's mace, but ....yea. The Rueful Axe was another good example. Stamina damage? Really? That's it?
So I can see what you're saying and at least in part concede your point. The rewards don't quite match up with the lore expectations.
No where does it say they directly corrupt the bow, it's through the blood of a vampire of cold harbour on the arrow that changes it's abilities.
I was under the impression, as I played through the MQ line, that it was their blood on the bow that would corrupt it's power. The way the Snow Elf and Harkon were talking about it led me to believe that the corruption would be permanent, but Serana and her mother seemed to think that the "prophecy" (or whatever) could be interpreted another way, and that by corrupting the bow it would end the world. If anything I just wrote was remotely accurate, then this left a lot of leeway as far as "game mechanic interpretations" go. It appears now, in hindsight, that no one really knew what was going to happen.

The scrolls were too ambiguous.
So arguing bow vs arrow corruption is a moot point. *shrug*

Just another case of Reward not matching up to the provided lore I guess. Awesome results to be sure, just maybe over hyped and a bit underwhelming.