Hard banning Airbnbs will for sure push long-term rent prices down, but not by an amount enough to make them affordable. We already have evidence from cities with active bans. Prices in NYC or Lisbon have not come down significantly.

We still have to wait a few years to see the real effect that bans have on prices. Lowering prices at most 3-5% by banning Airbnb won't make anybody happy and will come with some negative effects like reduced tourism (and other economic activity), which is a very important part of Spain's GDP.