The Eternal Noob

[Hoofhurr]

Making us generically good at killing everything turns the world into a dull place.

Making us generically good at killing only those things that we've been killing since day one doesn't scream excitement to me. The exciting thing in your example is the surprise of the troll showing up unexpectedly, not the fact that its a troll which, upon identifying, you decide to either run from or fight depending on whether or not you've ever fought trolls before. There's not much of a decision process there that I can see. Your character has fought trolls before, your party mates haven't. You stay and fight and they run away; this despite you probably end up fighting the troll exactly the same way as you were fighting the frogs.