If you magically create 100k affordable homes, you'll find population growth to fill up those homes within a relatively short period (<10y). If you magically remove 100k homes, you'll see population drop. So population growth isn't a complete measure of demand. Rather it just says something about how much the housing stock reasonably can accommodate. If you build nothing, population growth will be minimal, but it doesn't mean all possible demand has been accommodated. It just means there's lots of latent demand that have no homes to move into.
It's more sensible to look at the growth of the housing stock verus existing housing stock. I read in this thread: 15k properties built over 10 years (1.5k per year), a metro that has houses 5.7 million people, 2.5 people per home, means there are 2.3 million homes. 1.5k homes per year on 2.3m existing homes means they're adding 0.06% housing stock per year.
That simply IS a drop in the bucket. It's peanuts. Most in-demand (capital/a-tier) cities aim to construct at least 1% a year. For example, Amsterdam grew by 15% in the last 10 years, despite very stringent building requirements, green zones that can't be built, height restrictions to protect the character of the inner city, swamp land foundations and various environmental, water & electricity capacity challenges NL is facing right now.
So yes, if you're constructing at a fraction of the rate of other in-demand cities, then I would agree that eliminating tourist apartments is a band-aid solution, not a root-cause solution that works in the long term.
As for the balance of tourism vs locals, it's a tricky one. I think one thing we shouldn't forget is that 1 tourist apartment creates a lot of meaningful experiences within a year. An average tourist say of about 5 days in a city means that across a 10 year period an apartment can accommodate either one family living there full-time, or 700 different families having a holiday experience in Barcelona.
Put differently, these 10 thousand tourist homes that will come on the market, will house 10 thousand households more, and will prevent 700 thousand households from renting them on a 5 day trip to Barcelona, adding only 0.04% to the housing stock (one-time) and changing very little about the economics of housing in Barcelona for (new) locals.
It's easy to hate on tourists, but being a tourist can be a wonderful experience, that is meaningful and valuable, and shouldn't just be dismissed as some annoyance to locals. Of course all should be in balance. To speak on a personal note: I live in a city that takes in 20 million tourists a year on a population of less than 1 million, I don't work in tourism and for me it's mostly an annoyance. I definitely think we shouldn't grow the number of tourists anymore in my city, I think the same for Barcelona is true. But I also think it's worthwhile to maintain a big chunk of current tourism, even if it's annoying to me as a local, because I have no monopoly on enjoying my city. We've restricted tourist apartments to renting 30 days a year (the number of days a local is on holiday himself, and rents out his apartment), and I think that's fine. No need to eliminate it altogether though.