Advent superweapon is good for nothing, as the cultural impact is so weak, can be neutralized by having a medium level culture in your empire.
Vasari has the second best superweapon, just shoot at the novalith planet, and take that out quick, then retreat. That's the strategy. It works to get starbases with government not to lose important planets, but it's better to kill the superweapons faster. Don't bother killing Deliverance engines as they rarely have huge impact, try to maintain strong cultural presence in your empire, having 1 broadcast center everywhere is more than enough..
Remember: there is no amount of defense that cannot be broken by offense. This is implemented to get rid of stalemate possibilities. Defense is always worse, as starbases can be killed without damage taken on your side, just think about bombers, they can kill all defense in no time.
Rebellion with corvettes and titans, I wouldn't say superweapons are more balanced, personally i hate the use of them, as Advent one is still ridiculously weak, Novalith requires expert micromanagement of defense, and the Vasari cannon cannot even be defended against, it will hit no matter what planet, and the unstoppable Vasari fleet will kill that planet even you get your fleet there in time..