Reliability comes from solar and wind power redundancy and geographic distribution. If your collection area is over a few thousand square kilometres it is very rare for there to be no wind and no sun. Make it a few tens of thousand square kms (which modern high voltage transmission achieves) and your reliability is higher than coal.
That there is North Sea wind power, howsoever intermittent, is a pure good. Tying it into a larger network makes it better. The solution to local deficits is more localities.
Transmission lines are not expensive at all compared to nuclear power. This nuclear plant cost $12B and it is a cheap one!
Compare that to the SunCable is budgetted at $14B, (AU $20B in the article = US$20B) which is an undersea(!) HVAC cable all the way from Australia to Singapore (3,800km!) AND a 3GW(!) solar farm[1].
By comparison, the distance from Spain to Scotland is 2400km. And when the wind stopped in the North Sea, Spain was setting records in terms of the amount of power generated from wind farms[2]
[1] https://www.intelligentliving.co/australian-undersea-sun-cab...
[2] https://www.evwind.es/2021/12/03/27-8-of-electricity-came-fr...