I'd always make a point of adding in the motherboard and RAM cost as a baseline here. Say an extra $300 (assuming we're not going completely low end).

So instead of $262 vs $488 your comparison should be $562 vs $788. Which means you pay ~30% more for ~30% more performance from your motherboard+RAM+CPU (the CPU being the dominant performance factor to these components).

Any clue on why that $1700 CPU is performing so poorly relative to the rest in the chart?

it's a 10 core from the time (2016) when that core count was somewhat exotic.