The radius is 3 and the maximum damage is 120. It would be ridiculous if Parasitic Bomb dealt any more damage or dealt it any faster.
Parasitic Bomb usually does enough damage to break through Protoss shields.
It won’t quite break through the shields of a fully shielded Carrier or Mothership, but if you cast Parasitic Bomb on a Carrier and dive-bomb it with Corruptors; then Parasitic Bomb will kill all of the opponent’s Interceptors, rendering them useless.
The mere fact that Consume exists makes any need to refill the Vipers trivial.
Landed Vikings cannot do their job as anti-air units, so Viper Corruptor Brood Lord is still extremely dangerous for any Terran relying on Vikings for anti-air.
13 range is reasonable in PvT considering that Liberators exist.
It isn’t a problem for Zerg either.