Seems to be a lot of situations where a bar or two is no service, and others where service is great. So as a determination of whether I can use the phone it is pretty meaningless.

Your experience will vary, but perhaps:

4-5 bars => 98% likelihood that everything is great.

1-2 bars => 20% quite good, 50% pretty decent, 20% quite bad, 7% bad, 3% no service.

How is something like that meaningless? That is immensely useful. You can also reason about it depending on the context. Downtown but inside a bar in a cellar? Or out in the country far from civilization?

That it isn't perfect doesn't make it meaningless.