The discrepancy might be solved if we assume that it's more about the quality of the route than the distance. The worse the route, the more the drive has to make "adjustments", and more adjustments means longer journeys. These can still be cut shorter by a faster hyperdrive, but it does explain a lot of the instantaneous travel seen in the media. Routes also start to have value in the right hands.
That's not really an assumption. It's an actual in-universe fact. This is why there are specific hyperspace routes established, such as the Permilian Trade route and Corellian Run. It's much faster to travel along established routes than more risky ones.
Well, that's close, but it's not quite what I'm saying. I'm saying if all things are equal, distance is almost irrelevant. So those old grids and calculating travel times based on the galactic XYZ coordinates can be tossed out. With the right route and a good hyperdrive you can get across the galaxy within a few hours.
Exactly. This isn't an assumption. The routes I mentioned are exactly what you're describing. Travelling along well established routes, are much faster (and safer), regardless of the galactic coordinates between the start point and destination, than more rarely used routes even if the distances are longer with the well established route than with the less used route. However, you're still not going to cross the entire galaxy in a matter of hours. Using the travel times listed on table 7-14 in F&D, travelling between sectors on one of the five main established routes would take only about three days, whereas using a less established route will likely take a week or more.
Which is why it apparently took a while to get from Tattooine to Alderaan (yeah, coulda been half an hour, but there was time to break out the chess game and the training gear, I think it was most of a day, at a minimum), but it takes minutes to get from Yavin 4 to ... [spoiler redacted].
Which brings us back to the problem of why the Rim is so much harder to govern than the Core for the Empire. Can't be purely a matter of travel time, a few days of travel, even a week, really aren't enough to interfere with a government's projection of force.