what about the slylandro's?  they don't have "crew"...

Well , the most important part of the ship - it's computer was dismantled from Vela's facility and later blown to pieces . There is no way of constructing new ships there anymore

uh, where did you get that from?  i don't remember the computer being dismantled from Vela's facility and blown to pieces.  in fact, i don't recall any mention of the said computer at Vela.

[VELA'S]

You guys forgot one important thing:

Remember how your flagship was able to, by the end of the game, with all the upgrades, pretty much walk all over the place unopposed ALONE?  They have a Precursor starship at their disposal.

... oh right, that thing got blown to pieces near the end.

... but remember

The New Alliance has a Precursor factory on Vela!!

The Chmmr managed to crack the slave shield.  They would apply the same technique to crack the slave shield around Earth's and VELA'S SLAVE SHIELD.  Now all it takes to for somebody (ie, the Chmmr or others) to guard that place long enough for a couple of Vindicators to be produced, crewed, and they can start kicking alian butts.