But what times of day or days of week were those flights?

Even in the past year (to use something way more relevant than pre COVID), on a route I fly frequently (SFO-YVR), I've had flights with an empty seat next to me, and I've had flights I needed to avoid when I finally made up my mind about a trip because they were J0.

Even last weekend, the return flight I wanted was J0.

I tend to fly out on Friday afternoons and evenings and return on Sunday afternoons and evenings.

And even knowing my data is all for the same times, it's highly variable on some routes, and completely full on others (like SFO-YYZ).

But it's certainly way harder to find J space, let alone R space, than 7 years ago.