Yes, you don't have to completely burn it to ash, but the amount of creature you have to seriously burn to kill it, assuming it's rather like a normal animal, is immense and because of the thickness of it's hide would require a tremendous, and long enduring fire that has the potential to do as much or more damage than the Kaiju. It's like trying to kill a guy by burning him with a Bic lighter. I'm sure you can do it if you're determined enough but it's not going to happen anytime soon.
I disagree. No matter what Batman we are talking about, we are ALWAYS given a fuckton of explanation/background as to why simply giving the GDP a billion of dollars is probably not going to be an acceptable solution for him. That is why nobody really questions this, since everyone understands why he does what he does.
The shit? The closest we've ever been given as to why simply cutting the GPD a check wouldn't help more than facepunching criminals is "they're really corrupt." That's it. The entire reason why dressing up like Batman is a rational solution to the problem of a city wide crime epidemic is three words, four if don't count the contraction. Even Batman's motivations aren't gone into deeply. "His parents were killed in front of him by a criminal." That's his motivation. Four words to handwave away why the billionaire playboy can't just throw money at the problem, and nine for why he'd rather dress up in leather and do it himself. We never get into the nitty gritty of why any one of a thousand plans would work better than dressing up like a bat and punching criminals.
And by superhero standards Batman is complicated. Superman, Wonder Woman, the Hulk, Thor? These are not deeply involved, backstory laden, explanation centered kinds of stories. AND THAT'S OK. Part of the premise of Superhero movies is that lone crazies in spandex are a more effective solution for the world's problem than anything else. Just like in Kaiju vs. Giant Mecha movies it is understood by virtue of the kind of movie that it is that the giant robots are the best solution. Wasting time explaining that is just that, wasting time. By buying a ticket to see the movie you have acknowledged that you accept the premise of the kind of movie it is. Same with a superhero movie. I don't watch Iron Man and then count it against the movie when it doesn't explain why Tony doesn't just start building Arc Reactors and end the world's energy crisis tomorrow, or use his amazing technical skill for other endeavors. No, I get that it's a movie about Iron Man.
Therefore, at least a BIT of a background, as to WHY they turned to building robots would have been nice imho. Why the heck are they building robots with so many other seemingly more practical solutions? Makes no sense! Ah, yes...because of x y z reasons.
Except that you get it. Just as much as Batman gets. During the initial Trespasser attack they talk about how even throwing the military might of the US at it it still took them six days and three destroyed cities to kill it. "They needed a new weapon," is a line right out of the intro immediately following this. And then they kick into the Jaeger building montage. You've got as much backstory as Batman ever got in any movie and it indicates that the country with the biggest, most capable military in the world still needed nearly a week to kill a category 1 Kaiju. That they needed a new weapon and giant robots were it and after giant robots we go from six days and three leveled cities to beating their asses right off the bat and winning.
Since they are creating an unique universe, I shouldn't be expected to fill in those blanks, anymore than I should be expected to come up with a background story for Bruce Wayne, to make sense of his action in the present as caped vigilante, wouldn't you say?
You're giving the Batman franchise WAY more credit than it deserves for giving Bruce Wayne backstory. Second, as much backstory as he gets Pacific Rim gets in that opening montage. Third, it's implicit in the franchise that giant robots are the answer and spending five or ten minutes of run time going over why nukes at the portal, burning, dipping it in acid, trouble with effectively covering the coastlines to protect them, it's all wasted time because... GIANT FUCKING ROBOTS.
The Force, lynch pin of the Star Wars saga... "It's an energy field created by life that binds us together. There aren't a lot of people who can use it." Yeah, watch Episode 1 again, not a lot of info on the force, but that dwarfs what the lightsaber gets. "A more elegant weapon for a more civilized age." Want to start talking about the many, many ways a lightsaber is a stupid weapon to use even with the force? Does that make the movie any less enjoyable? Does it make the world being built any less rich real and fun? No, because when you see the movie poster with a guy holding a laser sword in the air and space ships flying around with the robots and the black kabuki helmet in the background you sort of pick up on the kind of movie you're going to see.
When you're making a film in a very particular genre there are conventions that go along with it that do not need to be explained. They are implicit in watching that genre. Unless you're going to be messing with those conventions then there's no reason to get into them and explain them, the audience is already on board by virtue of having bought the ticket.
I'm not saying this isn't a fun bit of mental gymnastics, it really is, but is it something to hold against the movie? I don't think so.