When comparing FCAS Vs GCAP planned entries into service, do not forget the Japan factor. Japan have been running a 5th Gen fighter program well before UK or France were teaming on the FCAS as it was known then.
Japan initially found positive inputs teaming with the UK industry that had a long reliable history developing 5th gen systems (and then with Italy).
That's why GCAP is planned to come earlier, unless something get wrong on the way.
Then, having talks around 2035 or 2045 just like if we were discussing interstellar events is plainly... Ridiculous. There are 10 YEARS b/w the two, with probably a large conflict happening during that interval of time that will see aviation modernizes drastically.
FCAS can not be compared to GCAP. If that is the plan, it's failed one, inherently.
You can see trace of this understanding in the late French military planning speaking of Very High Altitude being dominant.*
[I used the term Hyperstealth (stealth + hypersonic) long ago but it might even only induce flying counter space mission where stealth is not a factor (since orbital assets have to fly... Orbits (at lest partially), you can probably choose often enough favorable airspace where to engage them outside of an enemy IADS).]
So the question remains: why does FCAS have to be extended that far into the fog of future wars?
Inherently that erases the clarity of the message being sent to our allies... But also toward our opponents.
*FCAS is neither advertised or known to be developed for such, even being contradictory with that.