@princearagorn1: Apologies for the (very)late reply.
That said, let's get on with it:
"I'm 100% certain the 'gravity didn't change' is mentioned nowhere in the series, ever. Since your argument is based on it, I'm going to ask for proof. Because when something is damaged, it's gravity has to change, near compulsory."
1. You're right, flat out saying that "it didn't change", is claiming knowledge I don't actually have. I retract the statement and apologize for the misunderstanding. The correct statement would be that there is no indication that it(the gravity of the planet) ever changed.
"I don't have to. When an object that size attracts has 10x earth's gravity, there's no other explanation possible at all."
Not true. I have already given one possible, other, explanation.
And to repeat a statement I've made before(in this thread iirc), we're talking about a universe where the destruction of the Moon had no negative impact on the Earth, where the Moon has(or at least had) a breathable atmosphere, and where moving faster than sound doesn't generate sonic booms. That the real world laws of physics are not entirely valid, is pretty obvious. And "real world laws of physics" is the only thing that you seem to be basing your statement, about the correlation between mass and gravity, on.
In comparison, the explanation of "magic"(for the lack of a better word), seems far more reasonable, all things considered.
"I was under impression that when the Bills made the planet explode, it's core imploded and formed the extremely dense but tiny planet. Similarly like when a star explodes it leaves behind a neutron star, or a black hole.
But even if we grant the possibility that King Kai used the magic to increase the gravity of the planet, we need to take into consideration what kind of magic Kai's were shown to have.
Kai's were shown to be able to increase the mass of an object like here for example"
1. Just like princearagorn1, you seem to be basing your statements on real world laws of physics, which is silly at best.
2. No, the Kais were not shown increasing the mass, they were shown increasing the weight(there's a difference). How, exactly, they changed the weight, is information we are not actually given.