It may not be possible to make a supply of explosive arrows and bolts and grenades during the first week or two but do you really need those during the first two horde nights anyway? Not only that, but will you even be able to craft the recipes for explosive arrows and bolts and grenades during the first couple of weeks anyway? If you focus your efforts on developing your water supply early on then by time you need lots of explosives you should easily have the means to craft what you need. I agree that it probably won't be possible to have explosives in time for your first horde night but in my opinion it has been OP for the first horde night anyway.