I was putting the question mark because Tom Hanks affects a Mississippian accent, which would not necessarily pronounce all of these words with a schwa.

"Ermahgerd" uses two different vowel sounds, and that ɚ sound is slightly different than the examples in the xkcd, none of which are ɚ.

Given all three of these items--xkcd, Forrest Gump, and the meme--are from the United States, it makes sense to think of them in that dialect context.

I realize that you're Australian, so perhaps you wouldn't pronounce all these words with a schwa, but one of the defining features of the Australian accent is the abundance of schwas that are added in places that American English doesn't have it--notably at the end of words. Arguably Australian English actually uses the schwa more than Forrest Gump (or Randall) would.

It's also probably important to remember that the entire population of Australia is roughly equivalent to the metro area of New York City. As of 2022, there were roughly 400 million native English speakers in the world, of which roughly 306 million are in the United States, so I'm not sure about your "most English accents" comment either.

That said it's a very common second language, and at that level there would basically be innumerable accents, but it would be nearly impossible to analyze relative vowel variance across at that scale. So, maybe!