cutting stuff could be very fun but now it is a bit pointless. It seems like the purpose of the long legs of the spider is that it doesn't damage itself with its own bombs. So if you cut off all the legs, it should be damaged by its own bombs. Traps should also damage the legless spider. (cutting off the legs is harder than just shooting it, so if you go that far you deserve the kill)
Make the spider more vulerable if you cut off the legs
Both. I think it's a bit annoying when you manage to cut off the legs and they should clearly be destroyed but you still need to finish them off.But for balance, in this case, I think the 6000 should require more shots from an arrow. Or you could have a 7000 that has a shield facing forward so you can't destroy it without cutting the legs off (thus stopping it from facing you and blocking the arrows).