Rotating mass is a suspect in this case, not necessarily the primary one but the lack of control authority in the presence of frequency fluctuations is the exact opposite of what you are suggesting. It means that something with a fairly large amount of source/sink capability caused a local stability issue. Almost all modern grid connected windmills are - and this may surprise you - connected to the grid using inverters because that gives them a much better chance at following the grid fluctuations than the older direct connected types did (which did have the potential to cause issues and which resulted in much higher start-up speeds than the present crop). These inverter based interconnects give response times that rotating mass based systems can only dream of, resulting in much smaller errors in phase and thus voltage tracking.

The European grid is stupendously reliable, far more reliable than any other power grid worldwide to the point that most houses and business do not have backup power plans (datacenters, hospitals, telcos and some others excepted). France is doing ok but do not pretend that without France this outage would have spread further. The Iberian peninsula has one of the weaker and heavier loaded grids in Western Europe, in spite of the above, they should have probably invested more into their infrastructure but Spain has a lot of other issues it needs to deal with which cost it a fortune every year in terms of crop losses, fires and floodings. Both Spain and Portugal (and to a lesser degree Italy and Greece) are in the line of fire when it comes to climate change damage.

Battery storage, solar, and wind can all operate as grid forming and provide synthetic inertia when provisioned to do so. Thermal grid services are not required for grid reliability.

Europe has languished on battery storage deployment, and as they rapidly deploy it, it will improve grid reliability.

https://www.energy-storage.news/energy-storage-significantly...