Paradoxnt you oviously have no idea on the premis of the defiant class.
In space just as a heads up, Life support(food heat and breathable air) would take up more energy then weapons hands down.. to break it down for ya, Galaxys had 1100+ people on board at any time sometimes as many as 1700 defiant has 100 at max(usualy 80 or less) thats around 15X the energy used on just Life support alone.
Navigational Shields and inertial stabalisers would also use significantly more energy due to the mass of the galaxy vs the defiant.
add on the extensive sensor, steller cartography and science facilitys, also dont forget the lighting and more.
Hands down the galaxy would use a crazy amount more energy to remain running.. your looking at more then 10 times the energy use just off basic ship funtions not counting defences
Secondly based on simple reality(and stated in star trek) the amount of energy used to project a forcefield is determined by the size and strength of the shield.. The Defiant is 1/8th the size of the galaxy.. to have shields as strong as the galaxys it would need 1/8th of the power .. in the case of the sov.. it would need 1/6th of the power.. if not less given the volume the shield would hold within.
Your argument for power vs ship Core size.. is totaly off base. The larger ships need a larger core just to run standard.
Im sure the defiant puts out less power thru its warp core.. indeed it must.. however given that it would have extreamly significantly less power usage.. im sure its still way overpowered. It is designed for war.. hands down any system not directly related to combat and survival im sure is disabled during battle.
For the person who stated that The Defiant was the only one with hull plating... its Standard with the ships design. The design was Classified till the Dominion war.. hardly expect a Captain of a none combat ship to have access to the detailed specs for a classified ship that wasn't expected to show
Personaly mod wise, id like to see a bit more survival related abilitys added to the defiant, with a perhaps 20% boost to hull and shields.. or at least shields.. and a significant boost to cost, the ship should cost similar to other cap ships