OP, I work in the lubricants field, on the science and engineering side. A couple of points I can offer are to keep in mind that automotive oil degradation and performance loss generally comes from 4 key areas: 1) Mechanical work, breaking down the viscosity of the oil, 2) acids and oxidants altering the chemistry of the oil and its additives, 3) physical particulate inclusion, and 4) excessive heat, which alters the chemistry of the lubricant and some of its additives.
Mileage is only a proxy for all of this - a rough average indicator of all these factors, but different conditions can have any one of these factors in play far worse than the others. Steady highway miles in temperate conditions are going to have far less of all performance-degradation factors here than you'd have in the same vehicle with weeks of stop-and-go commute traffic in a Pheonix summer. However, the same highway miles in temperate conditions in a high-mileage vehicle will have a lot more blow-past chemical and particulate contamination from the pistons getting into the oil than that vehicle would have had at lower miles, and it will degrade that oil much faster.
Oil changes also aren't only about protecting from friction damage - it's also about minimizing deposit formation (sludge, varnish, etc), and keeping seals and gaskets protected.
There's also the issue of time. Acids and oxidants can be particularly bad for oil with time, mostly degrading its viscosity (and how well it keeps your car's parts from grinding against each other as a consequence), so even if you have a vehicle that is getting less than 5k miles a year (like a classic/hotrod, etc), change that oil out annually or every six months, no matter what is advertised by either the oil's manufacturer or the vehicle's. Even low-milage acid and oxidation accumulation can cause outsized impact with time. However, the higher the quality the oil, the better the synthetic molecules and additives will be engineered to tolerate all of this, and the larger your margin of safety before it becomes problematic. Oil quality absolutely does matter - don't let anyone convince you otherwise. But you can get reasonably similar performance out of lower quality oils just by changing them out at more frequent intervals.
Changing oil and filters early and often manages all of this. I run some pretty premium synthetics, and the absolute best filters I can find - and I still change my oil out at 5k miles or every 6 months, without fail. If I'm doing a lot of towing, off-road driving, or stop-and-go driving, especially in the summer months, I'll change it out every 3k miles - especially if I see the oil darkening.
A final point - what I do is for absolutely maximum performance for long-term durability and reliability of my vehicles. They won't suddenly break down and die if I go a month or two long, or get a couple of thousand miles overdue. But these maintenance norms absolutely do extend the life of a vehicle. Most people simply won't ever notice any benefit if they're getting rid of a vehicle every 3 or 4 years. You only see it if you've got something you value, and don't intend to part with.