Of course we shouldn't entrust all new construction to giant companies.

That's just another form of restricted supply.

Missing middle housing should be legalized (and now is legalized across good portions of the city, and a number of small projects have been approved).

Why aren't those affordable, you ask? Because even small local developers play by supply and demand. Joe from down the street does not have any special interest in giving you a sweet deal. Plus they have to pay high land costs even if their construction winds up cheaper and they don't have amenities.

It's also the same principle behind new cars not being affordable while used cars are, you need to make enough new stuff that people start moving out of the old ones, thus lowering the price.