Thing is, kaijus go through the Breach every time with no ill effects and that dimensional tear can be inferred to have an absurd amount of radiation being pumped out of it at all times.
That second thing is probably a valid anti-feat, but I'm not sure we can just assume any dimensional tear has a lot of ionizing radiation coming from it, unless there's a statement of that.
We can because the novel directly states the Breach is atomic in nature.
It was also explicitly stated by the first film’s screenwriter, as well as in the novel Uprising Ascension (although this seems to be using it to explain why Raleigh died, which isn’t the case in canon).
I don’t think I agree that they can take multiple shots from Plasma weaponry. Knifehead was significantly damaged by a single shot, to the point that Raleigh and Yancy were convinced they had killed it, and the very next shot from the weapon killed it. Leatherback didn’t fare much better, with its arm being completely taken off by around 8 shots from the cannon, and the creature itself seemingly killed in about 14 (and notice it only took about 3 to actually penetrate through Leatherback’s full body. And no, the power of the Plasma caster wasn’t improved, only its warmup times ). The rest of the Kaiju in the movie never actually take the plasma caster. Additionally, this still wouldn’t matter much as plasma typically doesn’t exceed 100,000K in temperature, whilst explosions from nuclear weaponry often have temperatures in the tens of millions to even a hundred million degrees Celsius
