That's right. HHL doesn't find x for Ax = b. It finds the result of a scalar measurement on x. Like you said, a garbage result is generated if the state is meas

That's right. HHL doesn't find x for Ax = b. It finds the result of a scalar measurement on x. Like you said, a garbage result is generated if the state is measured naively. It's rare for quantum algorithms to be drop-in replacements for classical problems. Take Grover's algorithm. Using it to search a classical database kills the speedup due to the number of calls to memory. Therefore, it will probably be used to attack NP-complete problems instead.