Yes, getting LBR data from production workloads is the whole ballgame for AutoFDO/SamplePGO and BOLT/Propeller. You cannot access the LBR on any EC2 machine short of a "metal" instance.
When it comes to PGO (vs. profiling the whole system) though it's worth noting that a lot of the speedup comes from things which are too trivial for us humans to consider.
When I profiled the D compiler with and without PGO enabled it became obvious that a lot of the speedup of PGO basically comes just from running the program, the choice of testcases made almost no difference.
When I profiled the D compiler with and without PGO enabled it became obvious that a lot of the speedup of PGO basically comes just from running the program, the choice of testcases made almost no difference.