You're ignoring that, it's entirely possible allow Y people to live there, without increasing numeric margins on rents. Instead, landlords/investors often look to maximize their profit margin as much as demand allows.
Which shows, that investors can be a factor to the problem, by either choosing to maximize profits for selfish gain, or keep rents minimized despite excess demand.
Yes.
Start b eliminating real estate investors and forcing landlords OUT of residential real estate entirely
This does absolutely nothing to address the situation that X people want to live where Y units are available, and X>>Y.