Yeah this was an eye-opening experience for me. I'm not necessarily humbled, but it points out two things to me (for the record I got a 35%).

1. The pareto effect holds true (I use a little over 20% of html's features)

2. There are a lot of interesting features in html that I should take advantage of more often

Look, most of the surface area it’s talking about is quite new, often still nominally experimental, and quite a bit not supported across all browsers (most commonly Chromium-only, with some Chromium-and-Safari-since-March-but-not-Firefox-yet; and note that none of them have an implementation but lack a Chromium implementation, even though there are a few possible features that meet these criteria—this is one of a few things that show the heavy Chromium bias in the survey).

Is it that high? If it’s more that 75%, then indeed shame on you.