1. It was written by Curtis Saxton, who is in league with Wong, and Wong helped write it, so therefore it isn't canon (I don't know how that's supposed to work)
Irrelevant. Being aproved by Lucasfilm is what makes something canon. Not who wrote the thing. If this point had any validity, we could easily dismiss all of KJA's "works" or any other EU author we don't like.
2. It contradicts all of the movies because we've never seen a 200 GT explosion in them (despite the fact that they never defined what they thought a 200 GT explosion in space would look like).
The Alderaan explosion makes 200GT look like a firecracker.
3. It is pure wank and there is nothing else in any canon at all suggesting gigaton yields for turbolasers. When I told them about the Dodonna quote and scaling down from the Death Star, they asked me "How do you figure out the Death Star's firepower?" I showed them the calcs, they said "Sorry, calcs don't count here, only feats, the feat is that it destroyed a planet, nothing more. Unless it said in canon that it was more powerful than minimum planet - busting power, it's not". Apparently their board rules support this.
Calculations are based on MEASUREMENT of the feat. The alternative is subjective bullshit. "Minimum planet-busting power" would require several minutes for Alderaan to expand.
4. The most ridiculous of all: Turbolasers can't be 200 GTs because that is enough to destroy a planet, so they wouldn't have needed a Death Star.
Absolute proof that you are dealing with a bunch of ignoramuses who don't know jack about physics. The dino-killer asteroid was a few orders of magnitude more than 200GT. Guess what. The Earth is still in one piece.
Later I gave evidence that the asteroid that killed the dinosaurs was over 100 Teratons. They said since it was 10 kilometers in diameter the energy was spread out and wouldn't destroy the earth, but a concentrated 200 GT beam would.
The DS beam was spread over more than 10 km by the time it hits Alderaan. They are just making shit up out of thin air.
Please help me come up with a way to explain this to them so they'll understand it and be convinced, I've tried everything.
These idiots won't listen to anything you have to say. They've already proven that.