I stand with his idea that to get kids to run 4:10, 4:05, sub 4, etc, that they can't think 4:20 is fast. If they think 4:20 is fast, there's no need to be running 4:05. If 4:05 is fast, and they want to be fast, then they'll train to break 4:05.
I can agree that some 4:20-30 guys may feel pressed because they feel like their accomplishment is getting diminished, but honestly, if you ran 4:20 in HS and feel so attacked by a T-shirt saying that 4:20 isn't really fast, I don't have a ton of sympathy. If running is such a big part of your life that you're personally offended by a T-shirt, but your PR is 4:20, that's kinda sad.
I think it'd be kinda cringe to see someone wearing it unironically though outside of a few circumstances. It's kinda just picking on people below you. It reminds me of those "3:50 your move Centro" shirts; I thought they were kinda cringe except for Hocker's friend who wore it at the trials. Maybe if a NP fan wore it to the state meet or Arcadia or something, but other than that it's kinda cringeworthy.