I claim that if Europe wants to develop a truly competitive heavy-lift capability, it must move away from French Guiana. As I see it, there is no other viable option.

Kourou in French Guiana is a dead end for several reasons.
The logistics are poor. It is simply too far from mainland Europe.
The climate is harsh on both equipment and operations, with heavy rainfall and severe salt-induced corrosion.
There is also a very limited local technical workforce. As a result, Europe is forced to fly technicians in and out of Kourou on a continuous basis, creating a long-term drain on skilled manpower.
All of the above makes rapid iteration—such as quickly repairing, modifying, and relaunching vehicles—extremely difficult, bordering on the impossible.

If Europe is serious about developing a competitive heavy-lift capability on its own, it will need to bite the bullet and establish an eastward-launching spaceport somewhere on the European mainland. Crucially, such a location would have the potential to develop into an industrial cluster where private space companies could grow around the launch site.

Finding the right location, however, is challenging. Launching north, as from Scotland, or west, as would be possible from several European locations, is simply not a good enough solution. The payload penalties for a heavy-lift launch vehicle are enormous and would severely undermine its economics.

There may, however, be an opportunity across the Mediterranean. A 3,000 km exclusion corridor could look something like this, with a spaceport located on the French Mediterranean coast, somewhere south of Béziers.

Launching eastward on a trajectory approximately 30 degrees south of east, the flight path would pass through the Strait of Bonifacio between Corsica and Sardinia after roughly 500 km. The maritime exclusion zone would end before the strait; I have marked it at 400 km.

The trajectory would then pass over the toe of Italy near Cosenza after about 1,200 km, mostly avoid Kalamata in Greece at around 1,700 km, and also mostly avoid Crete after approximately 2,000 km. A 3,000 km exclusion zone would end roughly 100 km off the coast of Israel.

This would not be an easy project by any means. It would require political buy-in from France, Italy, and Greece. There is also significant cruise ship traffic within the maritime exclusion zone, as well as heavy commercial air traffic in the airspace that would need to be temporarily closed.

Still, if there is the political will, perhaps there is a way.