i am a huge fan of the akira and was sad to see it so low down the pecking order. From everyting i've seen about the ship its meant to be only slightly smaller than the soverign and built as a warship.
Heres hoping they put in some sort of refit option so we can upgrade the ships we like to tier 5 for endgame content.
Federation ships aren't warships, every single one houses crew quarters frequently described by other starfarers as some form of 'luxurious', and are utterly stuffed with scientific equipment and even holodecks. Their hulls are covered in freaking windows, and even the little Intrepid-class can maintain and produce it's own small fleet of shuttlecraft while tooling about on the other side of the galaxy.
By comparison the Defiant is a flying brick covered in guns. The rooms are as close to barracked as Starfleet has ever shown, there's sod all recreational facilities, if you want to see outside you walk out an airlock because your window is an armour plate, and if you're lucky you might have the scientific facilities to work out that planets are roughly spherical.
The Federation is just plain better than its rivals, they've been building armed explorers and fighting wars with them against full on combat vessels from opposing empires. The Defiant is what happens when the gloves come off; a tiny little freaking death machine.
This is pretty much the best thing I've seen all day.