I disagree that 1% chance is a jackpot but 5% isn't. I'm using jackpot as an analogy for the emotional impact of a rarer, higher tier win mechanic - I don't think specifying a number is useful here. That feeling can happen with a range of different rarities.

I'm not following your point about nat 1s, free gimmes or supply and demand.

I think we're using very different ideas of game design. Are you using good design in the sense of like "tactically balanced"? I think of good game design as setting up and meeting player expectations for fun while minimizing frustration.

The game sets up rolling 20 and critting as a win big moment. To occasionally then deny players that fails to meet expectations and creates disappointment. That's why I think it's bad design. And why most people don't play it as written.