That’s completely wrong. Compliance is much better for 30 mph roads, it’s pretty much the other way around with 50% exceeding the speed limit but 82% driving less than 35. Meanwhile only 15% of drivers on measured roads follow 20 limits, with 50% of drivers going above 25. Source
It should be noted that the “measured 20 roads” are primarily roads that don’t have traffic calming measures, which were designed and built for 30 but have had 20 signs slapped on them - but that’s exactly what this proposal is about. When roads are built with the official recommended traffic calming measures, when the roads actually feel like 20 roads, then there’s compliance. But that’s not what they’re doing here.
It still means fewer pedestrians crippled.
That’s an issue in specific areas, not in every single part of every single 30 limit.
If you want 20 mph roads, then build 20 mph roads. Provide ongoing training for drivers. Don’t just slap a sign up and jerk yourself off over it.