I think the largest range I've seen that wasn't very obviously from some resume harvester or z-tier recruiting firm was $30-40k between the lowest and highest, and it didn't seem to grow all that much as the upper band number increased (e.g. I distinctly remember one that said $180-200k). These $50-500k ranges simply don't happen in reality.

I've seen plenty that go $100-350k, especially when it looks like a company is hiring a few people... Useless to a candidate, but not dodgy or malicious.

Not useless at all. Every candidate will start with the expectation that it will be explained why they did not hit the maximum of the range. They also know the minimum.

Not useless to a candidate, since they know they will earn at least $100k. This is a very useful signal to the labor market as a whole.

Take a look at Netflix, here's one at random but I believe they're all like this:

https://jobs.netflix.com/jobs/294103648

"The overall market range for roles in this area of Netflix is typically $180,000 - $900,000."