I mean, most of them are hosting "locals" as in residents who live in Barcelona. I just took a look now and there are at least 90 apartments available on Idealista for rent in just the ~3 surrounding blocks around Sagrada Familia.
So while in general the whole "touristic flat rentals" stuff is clearly hurting the city, maybe over-dramatizing the impact isn't super useful. Overall the situation sucks though, as prices seems to still go up :/