When you need to use them, you can dump all your stock without any sort of cooldown, as fast as the AP will let you.
You can - but then you won't have any left for the next encounters...
The best way to balance grenades is to make them rare, really rare, so that players usually only use them in kind of emergencies and not spam them.
Special arrows though are the archer's bread and butter and I don't find them overpowered. On the opposite, their very existence make the archer a viable build in the first place. His signature is that he is pretty flexible but only medium-powered build. His damage output is average, his skill power is average and his defensive values are average. Wtihout the possibility to use a lot of special arrows this build would imo clearly be disadvantaged compared to other builds.
And if you really want to cripple yourself in every possible way in combat I suggest you might create/use a mod for it.
