As long as grid operators keep an eye on their inertia figures and fault current handling this is great news.

Synthetic inertia created by inverters can maintain grid frequency, but they cannot handle fault current. Without the ability to ride through disturbances, downstream protection equipment will fail to work correctly. If you hit a semiconductor with 10x its rated load, it needs to shut down immediately or it will be destroyed. The turbine at a nuclear or coal plant can take a serious beating for several cycles before it would be forced to trip offline. The machine is massive enough to absorb any damage without losing its overall functionality.

We need actual synchronous machines spinning with heavy masses. They don't need a carbon-emitting prime mover on the other side. They just need to be connected to the grid. They also need to be placed relatively close to the inverters (same plant/substation) or they won't provide the desired support.