Ignoring the Catalan issue specifically: the members of the EU are themselves states so would be unhappy with the precedent of any of the other states breaking apart as it might set a precedent.
Thus none of the arguments against Scottish independence from the UK was that Spain said it would oppose Scotland joining the EU on its own as that would be a precedent for Catalonia. (Scotland might get a “sympathy pass” if they tried it post brexit, but perhaps not).
I agree that the EUnwoukd operate better with a larger number of smaller members but there’s no chance of that in my lifetime, unfortunately.
Thus none of the arguments against Scottish independence from the UK was that Spain said it would oppose Scotland joining the EU on its own as that would be a precedent for Catalonia. (Scotland might get a “sympathy pass” if they tried it post brexit, but perhaps not).
I agree that the EUnwoukd operate better with a larger number of smaller members but there’s no chance of that in my lifetime, unfortunately.