That's just pro-landlord propaganda but i've never seen actual evidence of that. I have seen evidence though that landlords and public powers conspire against the population to gentrify neighborhoods and drive prices up, leaving tons of apartments empty so they can make more money speculating.

It is more nuanced; the private investors want to make profit as quick as possible, they do not care about long term development of the area (many politicians either, they might not be in their position after next election).

The private investors won't do infrastructure either - it is expensive - so they want to build where the infrastructure is already in place. So that's why we see trying to increase density.

So the zoning rules are there as a conterweight to this.

Absolutely not. Investors fight with tooth and nails to keep the prices up because it's more profitable than building.

And in many cases it's private investors buying houses for speculation (either by increasing rent or by using them for AirBnBs) the ones that drive prices up, not an increase of supply.

In any case, my point is that applying market rules to housing does not make sense, it's not a competitive market at all and never can be.