Btw, the king actually CAN die from a skull tower… the explosion damage radius of a skull bomb is larger than the king’s throw-back radius.
And, as oPelle already said, a high lvl skull tower really throws a LOT of bombs, in rapid succession… hard to impossible to kick back every single bomb, especially if several skull towers fire simultaneously.
And most important, skull towers were never meant to do much damage to the king. Rather they were created for wiping out whole armies in a matter of seconds, leaving the king lonely and vulnerable…
Also, bomb towers (especially with long range boost) throw their bombs quite far, and within a busy situation it can still be very hard to kick back all the bombs, and also you might not even notice them at all when there’s going on too much on the screen (other towers firing, hostile wave troops attacking you, you need to concentrate on right spell timing and spawning troops, …).
Anyway, having said that, a stun tower might be interesting… though, I’m not sure how effective it would be (due to hero scream / wolf howl!), and also there’s already mummies, stunning ogres and various slowing down units (e.g. frost trap, froster, boosted arblaster, ice tower), so another tower with stun ability might be a bit redundant maybe?
Not sure what you mean with sonic blast tower?