It has cloaking devices, yes - look at ESB; when the Falcon disappears off the Imperial-class Star Destroyer's sensors, the captain assumes the ship used a cloaking device and doesn't even attempt to keep searching, no 'activate the cloak disruptors' or 'engage the tachyon repulsion nets'. So if there is a counter for cloaking technology in SW - a single type of specialized sensor that was both rare and extremely expensive, it is not something commonly included in a Star Destroyer's sensor suite. Plus, they're rare (cloaks). In the Dominion, cloaking technology is so well-developed and commonplace that they hand it out to mid-level spec-ops assassins and mount it on all their starfighters. Again, you're taking game mechanics as canon, whereas cutscenes show Wraith blasts as very destructive, and they are in-universe designed as anti-capital ship strike craft - until the Republic starts deploying specialized cloak-detecting ships, or refits their entire fleet to carry said specialized sensors, they're sitting ducks for any Wraith pilot with a charged power generator.
There were no survivors of Korhal. It took 49 years for the radiation levels to drop low enough to where humans could walk on the surface without dying.There's one difference between a BDZ and a nuclear bombardment of a planet: The nukes leave survivors.
The 200 gigaton figure was canonized by one book, by one author, whose extremely flawed and generous methodology of arriving at that figure has been infamously dissected and discussed to death ever since it was published. Diehard Saxtonites still defend it, but they're the only ones.And yes, I agree that they pack a punch above their weight class and can take hits. But only in their perspective universe. When each turbolaser shot is considered the equivalent of several Terran nuclear missiles: I feel that the battlecruisers are going to be greatly outclassed.
It's considered canon, so I have to use it. Otherwise I'd just cite the fact that Battlecruisers can't one-shot Marines in game and this entire argument becomes moot.