I'm starting to think the Starbase build time was deliberately left that fast for the beta.

It makes no sense if you compare it to other build times, Superweapons especially that actually take quite a bit longer to build than Starbases.

1. Build starbase in enemy gravity well.
2. Queue 3/4 shield/hull/armor upgrades.
3. If Advent, queue mass disorientation.
4. Queue weapon upgrades.
5. ???
6. Profit!

You make a valid point, but this tactic is far too successful.

It really shouldn't take half a fleet to destroy something in construction.

I made a post earlier about a game where the AI decided to start building a Starbase in the middle of a fight.

First the constructor "starts building" right before it is destroyed, simply disappearing and making the damage done irrelevant. Annoying. Then the 6 Destras and the high level Radiance with Cleansing Brilliance who turn focus fire on the "construction site" are unable to destroy the base before it is built. That's 110 fleet supply points worth of ships including a high level battleship with a level 6 ability. The thing is...

A massive Starbase was casually built from scratch under direct focus fire during a skirmish!

The issue here seems to be that the starbase has shield mitigation while it is being constructed.  (Obviously this is less of a concern if you're playing Vasari, but it still matters somewhat.)

I was too tired to run the math last night, and I've lost what I was working with (cut to clipboard and forgot to paste somewhere), but I was looking at about 160 DPS to kill a starbase before/as the first upgrade completed.  Call it 300 if you want to destroy it before/as it's built, as building takes about 25% longer than an upgrade.

Feel free to run the numbers yourself.  For one, I didn't consider the rise of shield mitigation (just calculated it as capped), as, again, I was exhausted, so in the first few seconds you'll actually do somewhat more damage than that.