I also reject "just building more", at least in already too big cities. I think a more viable long-term approach would be to foster the economy in such way that creates more jobs in smaller cities. Spain needs cities like "Düsseldorf" or "Austin".
I am sceptical of this kind of central planning. Fighting against organic growth and artificially trying to increase jobs in other cities seems like it would cost a lot more as a whole than trying to solve the problem where it actually exists.
You are right to be sceptical and should be. However in this particular case, what we see today, is exactly the outcome of central planning, from the previous regime that ended in the 70s, which effectively decimated industry on the countryside and forced everyone to live in large cities.
