Seattle has a similar problem where we do have a large number of new units going up, but some places are still seeing upwards 50% vacancy after 3 years... because the new units aren't aligned with market demand. I'm talking luxury apartments downtown when the growing demographic is frugal-minded mid-20s/30s interested in neighborhoods 10-20 minute away from downtown. Even constructions in the right neighborhood end up being a net loss of desirable units when the rent is sky high.
So, yeah, more development might help Berlin, but it will be more effective when accompanied by rent camps and strengthening of social housing banks. Otherwise you are just feeding the bubble and exchanging one population by a wealthier one.