should be, within reason, able to deliver as many of them as ESA wants
Where "within reason" means 1-2% of launches Falcon 9 can do. Again, if Ariane 6 internal costs were $20m and they could do 150 launches/year, you would see actual competition and prices going down, and Jevons paradox with a lot of new launch demand.
If ESA was actually a commercial launch company, this would be different, but they're not. (Arianespace _is_, kind of, and _it_ should be far more concerned about this).
For practical purposes the number of Ariane 6 launches is gated by demand. Over the long term you'd probably expect it to be 5 to 10 per year, same as Ariane 5 used to be.
That's because SpaceX is soaking up its spare capacity with Starlink. I expect once that market is saturated SpaceX's launch prices will begin plummeting, as it seeks to maximise volume through market share.
More critically: SpaceX discounts for volume contracts. And it's the only launch company offering the kind of cadence populating a LEO constellation requires.
It's not about the ESA as a client and those bespoke science payloads; it's about (mass-produced) European satellite constellations, and similar high-volume, low-cost payloads.