I think a lot depends on what someone considers an upgrade.

If upgrade has to mean an executive suite with a separate bedroom that closes off from a living room -- or even something more grand and luxurious -- then, yes, upgrades will be rare. At most hotels, there are few such rooms, lots of other elites wanting them, guests who are really valued by the hotel because they return frequently or can bring in other business, and even guests who actually pay for suites.

But if upgrade means a better room than the booked category, then upgrades can be much more frequent.

At full-service properties, I'm usually on high floor, often on the side of the building with a better view. Sometimes, it's a larger room. I rarely stay at Fairfield, but when I have, I usually get a room that's similar to what you would find at Springhill Suites, not just a basic room, At Marriott Vacation Club, I know I'll get exactly what I booked, nothing more, nothing less (because that's how the vacation club business model works). I did well with SNAs in 2019, but not so well since then.