The article explains the size differences very well.
And it mentions that mars' impactor only remelted half the surface, while earth's impactor melted the entire surface of the planet. Which is supposedly why earth's magnetic field stayed axially dipolar.
From what I've read, the size, speed, and angle of whatever hit the earth is not settled. But if we know that, as you say, half of Mars was melted, while all of Earth was melted, then that should put constraints on how the impacts differed, which is what I was curious about and is not part of the article.
Without knowing all that much, I know that Earth was much more massive than Mars even before Theia impacted. I assume with the extra energy available, it would be much more likely to melt all the crust. Also, our plate tectonics is still going on, so any evidence of a thin area of crust would be erased by now.
also it's interesting that the crust of the moon have differences between far and near side. I read somewhere that this could be explained very easily with a low speed impact of a second small moon when the moon was very young.
There was a recent paper proposing that the near side of the moon looks melted because the surface of the Earth was temporarily about as bright as the sun for a while after the impact.
And it mentions that mars' impactor only remelted half the surface, while earth's impactor melted the entire surface of the planet. Which is supposedly why earth's magnetic field stayed axially dipolar.