It won't fix everything, of course, but it will give us a much more normalized market to then attempt further reform on, rather than the current one which has more in common with a casino floor than a market.
For one, the city did not "ban housing investors," they banned some investors from purchasing a subset of homes, which is already weak, and only made weaker by the fact that the first study analyzes only a few months of market activity under that new restriction.
That being said, both studies do indeed conclude that a link cannot be established with certainty between the policy and house price reduction.
> Results from the difference in difference analysis show that the null hypothesis that the policy effect on home prices and days on the market is not significantly different from zero cannot be rejected. This means that it cannot be concluded that the buy-to-let restriction reduced housing prices or increased the days on the market.
However, this is one city, not in America notably where the problem is at it's worst, and they did not restrict lower income housing which is the most liable to be outbid on by private investors and rented, so I would hardly say these two studies by themselves utterly disprove anything in the way your dismissive comment implies they do. I don't think a partial restriction on a housing market in one metropolitan area out of the roughly ten-thousand currently on the planet is definitive proof.
Ultimately, these empty homes are investments and sometimes investments fail, and if they're big enough sometimes those failed investments cause people to lose a lot more than what they invested. That's literally the definition of investment risk. We can't keep doing status quo with this shit while the market continues to sail further and further out of reach of all the people who actually need what it's selling.