To go a step further for GSM (I don't know precisely for 4G, but I suspect it is the same) the base station determines both handset dB/SNR/Quality and commands the handset power which usually is limiting performance. It is likely this setting that allows the handset to report its "number of bars"...

So if you don't let them lie on the handset... it's likely that the network providers would just start lying to the handsets at an even deeper level than they already do. Just get the marketing silliness out of the way at as high a level as possible so engineers can make our coverage better.

there are at least 4 values.

rsrp, rsrq, sinr, rssi

rsrq is probably the important one. You can clearly see usage of the cell tower with that.

Number of bars (1-2 vs. 4-5 or whatver max is) seems to give a pretty decent indication of latency and bandwidth to me. I get that it isn't perfect.

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.

In my experience, two bars perfectly indicate the threshold of ”there's service, but no service at all might've been better—at least there wouldn't be false hope.”