I can't take this … Luffy weak against heat & sword? If we compared rubber with human skin & flesh, which one more weak against heat & sword? Not to mention Luffy will possess strong COA and already have red hawk attack (use fire).
What do you mean, you can't take this? Luffy being vulnerable to heat and cutting attacks is established, he just learned to protect himself from weaker attacks. Hody freaking Jones was already enough to break his Coa. Similar, the flames produced from Red Hawk are hardly comparable to a magma fist from Akainu. It would surprise me if Oda wouldn't make that a thing when Luffy fights him near the end of the series (if only to show how he overcomes one of his greatest weaknesses on the highest level, shounen style).
This hunch just leads me to believe Blackbeard wants to tear apart the World Gov't, but instead of for a good reason, he'd probably do it with the intent of trying to descend the world either into madness or subject it to his rule.
Blackbeard destroying the World Government would be amazing, but I worry that I would probably start to root for him if he does.