It's unlikely that there's any such thing as an actually affordable apartment in a major world city, unless we've moved the method of allocation to something like lottery or waiting list, in which case it's only affordable to a lucky few.
I would encourage anyone who thinks that luxury apartments are for the rich while single family houses are normal to consider the relative luxury of life in the actual structures (not location). You'll find that, as structures, luxury apartments are much less luxurious than lower-density uses of the same land.
The only tax that a squatter does not pay in contrast to an owner or renter (indirect there) is "ground tax", which is a negligible amount anyway.
And the only interest which the "owners", mostly in form of offshore companies, have is to make huge amounts of money at the cost of the city, so I don't have a single tear left for them.
No. Berlin problems mostly stem from the city government colluding with investor scum to build luxury apartments instead of actually affordable ones plus doing their very best to e.g. kick squats out (which help keeping down rents for all neighbors). Berlin government could easily break the necks of the investors and protect the population instead, but especially the SPD has chosen not to do so - and sell off priorly city-owned prime real estate to investors.
The investors now do "Luxussanierungen" (basically, thermoclad the houses and fix the more egregious stuff like bad wiring / plumbing that the city government had neglected over decades) and price out all the lower-and-middle-income people.