Sometimes parts are weaker than the whole. The strong economy is possibly part due to investments made with the assumption that Catalonia would be part of Spain for the foreseeable future.

Would London have been the de-facto financial hub of Europe, if people knew Brexit was coming?

I'd bet you London will keep being the financial hub of Europe long after Brexit.

Everyone on Earth has a petty identity. If we allow secession just so every self-identifying group can 'rule' themselves then we encourage those petty identities when we should be discouraging them and instead encouraging universal humanism.

Germany is a federated state, stark differences between the regions (the dialects vary a lot, but not as much as the Spanish and Catalan languages differ) but it does work because the government is not centralised like in Spain or France, and the Bundesländer have their say there's a lot of respect for each other. Spain's PP has always shown disrespect to any federalization and autonomy of the spanish regions.

Except the government in Spain is not centralised at all. The comparison with France is just...

IDK where are you getting this ideas but is mostly the opposite. PP is disrespectful about everything but that doesn't mean that there's no autonomy, there's a reason why every region has an "autonomous government" and are called "autonomous communities", basically because they have that autonomy.

More: https://en.wikipedia.org/wiki/Autonomous_communities_of_Spai...