It does hold true for some systems. Wind turbine generator controls can provide virtual inertia over very short time scales (a second or few) by exchanging energy with the turbine rotor. You can also provide primary frequency reserve in the negative direction (load step-off) using exactly the same ramp control that steam plants use. Typical ramp rate is 100% of rated power for a 5% change in frequency.
However, in order to provide primary frequency reserve in the other direction, you do need additional local storage. You don't need very much. Just 10% of rated power for 15 minutes gets you to very deep renewable penetration.
The trouble isn't with the technology, its with the economics. Once you set a sufficiently high price for frequency support and primary frequency reserve, suppliers will show up.
However, in order to provide primary frequency reserve in the other direction, you do need additional local storage. You don't need very much. Just 10% of rated power for 15 minutes gets you to very deep renewable penetration.
The trouble isn't with the technology, its with the economics. Once you set a sufficiently high price for frequency support and primary frequency reserve, suppliers will show up.