No, B is compact, not economy. The Kia Rio is listed as an A - but considering that even a Chevrolet Spark is a B, it's surprising - especially as a Rio would be quite nice compared to a lot of B cars.

Focuses, some Dodge Darts and even 2.5 liter VW Golfs can be Bs (or YBs).

Notwithstanding that, the OP was given a car in the B category so has no contractual right to complain, but Hertz's classification is a mess. There is no practical difference between a Corolla in C or a Focus in B.

So while I don't think that the OP has any right to complain, I wouldn't bother with A or B unless I truly didn't care about what I drove, or rates were absolutely insane.