I don't think Implosion ships are OP, and yes I have gone into a system and watched an armoured golem, and two MKV Devastators reduced to smidgens of health in seconds. However this to me just means I should have been more observant and sent fleetships to deal with those first.
(I was feeling particularly powerful with my MKV Dev Fab and the massive amount of HP and firepower these ships had, so I just wandered into a border planet to the core world to test them out. An expensive decision to say the least)