It's best near the equator (and starting eastwards) if you want an equatorial orbit because then you get all the rotational energy from earth for free.

But if you want an polar orbit, so 90° to earth's rotation that passes over north and south pole, you are not just missing out on the free speed but the rotation perpendicular to the direction you are going actually is a problem you need to compensate for with more energy spend. But the further north (or south) to the pole you move for your start the less influence has the earth's rotation. The perfect scenario here would be a start exactly from the geographic north pole for no interference through earth's rotation.

This is more about having the ability to launch any payload at all from Europe. Especially so we don't have to be 100% reliant on launch sites controlled by the US or the one on other side of the Atlantic in French Guyana. If anything, the more the merrier, continental Europe should have the capability to launch from both the north and the south.

Launch sites away from the equator are good for some different orbits. The Molniya orbit, for example, is very useful if you're trying to observe areas at high latitudes

A lot of sats head to polar or sun-synchronous orbits, both of which benefit from being very far north or south (less west-to-east velocity to cancel out).

Rocket Lab launches into those orbits from New Zealand all the time. The ESA goes straight north from Kourou sometimes, but that site is on the equator and so is much better suited for lower-inclination orbits.

Equatorial efficiently is so 1960s.

The founders of rocketry just said, "hold my beer".