I agree with you on the defiant, its just not a defiant w/o pulse phasers, and why have 3 phots when 2 Qs are better?
My other ship is an Intrepid, phaser XFs in the two front and the omni mount, phaser IXS on the nacelle mounts, and 2 Q torps pointed foreward. I rarely ever upgrade impulse, usually use the engine mass for a big enough warp core to power everything, and maneuvering thrusters to make the ship perform an HET without clicking the HET button (available only on the Defiant and Sabre currently
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I only fly the heavier ships (Galaxy, Nebula, Soverign) if I have to, since its like flying a brick even with a full thruster refit.