I'm playing against four AI's, one is a Vasari Rebel. Their Titan ship cannot be destroyed. I've focus-fired 90-100 bombers, as many fighters and the entire fleet on it.. I can take the shields down fine, but the hull isn't breachable in any way.
It has this ability, it seems, that restores thousands of shields and hull every second.. it's just not possible to leverage enough damage at it to take it down.
I saw a Vasari Loyalist AI lose an entire upgraded fleet against it, now I've lost one as well.. Not the entire thing, but like 10 level 10 capital ships.. Anyone else see this happen?