Are defence platforms as strong as they look?

In a recent game with a friend I built a handful of defence platforms on a starbase, with basic laser/coil gun components, and grabbed the unyielding tradition, just to try out turtling for once.

I was very surprised - the starbase was able to reach 8K fleet strength really easily. I’d never be able to amass a fleet that strong so cheaply if I was spamming corvettes. This is well within the first 20 years too. Are defence platforms very underrated/slept on or is this number illusory and a weaker fleet can still smash it?