Primary frequency reserve kicks in to automatically throttle back dynamic sources. Typical throttle rate is 100% throttle response per 5% frequency deviation. Inertia (both real and virtual) just slows down the system response enough that PFR will be effective. Just about every steam plant, combined-cycle plant, and gas-turbine plant participates in PFR. There have been proposals for inverter-connected systems to participate as well, but I don't know how common it is in practice.

Once upon a time the rated load-step response for a sub-grid in the US was a step-off transient of a nuclear power site going off-line.