They're guided, how can they miss?
Guided with what? An aircraft that's within range? Special forces? I would recommend making sense. Artillery needs spotters. Spotters need to get close to the target, which implies either physical presence within LoS using infantry or aircraft, or using satellites. But spotting with satellites during war is extremely difficult to downright impossible, considering satellites are even alive when the war has reached the point of using nukes, whereas going 200Km deep behind enemy lines with infantry to find a SAM site that's always moving is simply a stupid suicide mission, and aircraft, lol, that's what the SAM is meant to stop, from twice the distance it itself will get detected.
Which means every country handing its sovereignty to Brussels, it'll never happen.
Not at all. I've mentioned it before. Security can be handled by some sort of a council where the big countries call most of the shots, like they do in the UNSC. I suppose France and Germany will lead here.
So France becomes the sole supplier at the expense of other national defence industries.
SSN is just one type of weapon. The same with a carrier with nuclear reactors. All other countries can pitch in everywhere else that doesn't require nukes, like fighter jets, SSKs, ships, SAMs, tanks, helicopters, APCs, IFVs, vehicles, small arms etc. A "nation" like the EU would require at least 2-3 types of fighter jets, at least 4 or 5 types of helicopters, 3 or 4 types of transports, at least 2 types of tanks, 2 types of IFVs for different terrains etc. There's plenty of space for cooperation with all countries participating in the R&D and production run, with states even competing to get a piece of the pie.