"it meant Rainbow DEFIANTLY saw Scootaloo as a sister, and would think she was weird."

ok, that's twice now. I thought the other one might have been a typo, but do you genuinely not know the difference between "defiantly" and "definitely?"

Also,

“Huh, I’ve heard of ponies chasing a purple dragon but this is ridiculous,”
... what? What does this mean?

The "I've heard of X but this is ridiculous" format of sentence only works when something is happening that is similar to a phrase that MEANS something else, or has a double meaning.
Like, if there was someone spanking a monkey, someone could say "I've heard of spanking the monkey, but this is ridiculous."
It's a way to point out a pun, not just "this is literally a thing that is happening right now."