Here's the real answer for based:

"Based" (corruption of base head - from someone who smokes base - street name for crack cocaine) was popular as an insult in rap / African American circles in the early 00s

Rapper Lil B got called it and decided on a whim to pretend the meaning was changed to mean something positive, started using it in this way, it caught on - mostly through the new York scene and its attendant twitter following

As all slang does in the last ~100-150 years, passed from black people to everyone.

Brain pilled is a reference to The Matrix f/t Keanu Reeves in which Morpheus - whose namesake is the God of dreams - offers to wake up Neo from his fake reality by taking the red pill - leading to the phrase "red pilled" meaning (a right wing variant of) "woke." 

Over time [x]-pilled became slang like how Watergate/ [x]-gate became a suffix to imply an imbrolglio.

Turn back now

Groovy

I can’t explain it, but this one feels very different from the rest.

And I still can’t read “tubular” without picturing a 90s TV show about skaters shot entirely with a fisheye lens.

I always took based to be a sort of ironic agreement with a slight political connotation, especially if something said seems particularly "bold."

Essentially "You totally understand who you're talking to (your "base") and the subject at hand; This guy/gal gets it; This is 'based' on hard facts" (especially when seen as controversial and few will admit it.)

You can understand how this became conservative-shitpost parlance for a while but thankfully (and ironically) has become more depolarized. So now I see it like "Yeah this fellow human being understands their fellow human beings!"

"Brainpilled" is just a stupid shift from the term "Red pill", coined by The Matrix and eventually co-opted by conspiracy theorists and others with intense socializing difficulties (that are everyone else's fault, naturally.)

The idea being you made a choice to "see the truth" when nobody else wants to.

It eventually spawned "black pilled" which is a ridiculously nihilist idea that "I see how everything really works now, and it's all terrible and there's zero hope."

And now we're at "brainpilled", like the movie Limitless maybe? LOL. "This person sees it from some genius angle us mere mortals can barely comprehend. They're playing 5D chess and we're still playing Candyland."

I dunno, some of it is fun and descriptive. Some is braindead. Language is like any art, it's like Bruce Lee says: take what works and leave the rest behind. :)

"X pilled" = a believer in X; i.e. they've taken the red pill with regard to X and see that it is true/good.

Based just means something like, “coolest of the cool”. They are unwavering in their conviction, and respectable in that regard.

My understanding of based is it's a way of showing respect for someone who did or said something controversial. You could disagree with what they did/said but you respect them nonetheless.