Full "ship tree" research, xinithium, and 20% ability bonus, and my starbases don't get 50 until they've killed something... I'm on 1.2, is there a big hp boost in 1.3?
Also, even with those 160+ defense numbers...
I had a Large ship with 200 *base* missile defense in my little "tweak stuff" mod (I fixed miniaturization while I wait for 1.3 to go "live" by turning off size modification. Geeze ships start getting expensive... well, to be fair, that ship did also have only 14 attack (was meant to be in range of starbases) so even with the modules that "plump when you cook 'em" a Huge hull can approach that). Got jumped on its way to a planet by *a* frigate which had something like 78 missile attack.
It promptly 1-shotted my armored behemoth (which had 49 hp) about 3 rounds in. You can pile all the defenses you can get your hands on, and pump them up with all the military resources you can mine, but the things *will* get shot out from under you in a couple rounds if the computer wants them gone, even if they only send one frigate each time. Well, that might take 'em a big longer, but they'll definately average better than a frigate per hp of the base even with level-up healing and all.
(even without ships packing extra firepower because of the no scaling bit I tossed in, you'd have to multiply the base defense numbers by a LOT before they're really worth more than dropping into place to assist an attack you're about to make, and then picking up to make the next one cheaper. For something that is supposed to "project power into enemy territory" it doesn't seem very economic)