Being able to buff your whole fleet's damage output and shield mitigation with a single Deliverance Engine >>>>> being able to destroy a single planet with several Novaliths (only because the AI doesn't really research the protection starbase upgrade).
I judge the super weapons by how I've seen them used in online play. Kostura's where brutal and could be deployed with very little effort (i.e. no pre-reqs on research other than 8 labs). I've never seen someone invest in a Deliverance engine and make a difference in the game. It MIGHT make sense to build a deliverance engine in a team game if you are pure eco and can invest eight civ labs into this one tech as there very little after 3 labs worth investing in. Chances are you fed away this money though so they could get 25% or more ships which last beyond 150 seconds.
Comparison of Hostility techs versus deliverance engine (excludes cost for labs and logistic space)
30% Laser/Beam damage upgrades: 11,000/1525/2550
30% Laser/Beam Plasma damage: 16,500/2300/3825 (excludes rate of fire increase on plasma which is 7 lab).
One deliverance Engine: 16700/1975/2725
Two deliverance Engines: 24700/2575/3225
Build a Halcyon and Rapture and buff your fleet by up to 22% rof and decrease their damage by almost 50%.
Build culture centers on your border worlds so you are fighting more often in your own culture for the shield mitigation benefit...
IMO if your building your own fleet it's hard to justify deliverance engines until after you've maxed out the permanent upgrades especially as it requires at-least 2 engines to keep the damage buff semi-permanent (3 to keep it overlapping and permanent)
Yes, if you can afford it and don't have much room to move up in fleet supply it can make a decent fleet enhancement.
I'd still like to see something added to the deliverance engine though. One less aggressive thought is to have it disable enemy culture centers in the targetted gravity well for the duration of the effect.