What you're saying is true because the market is severely distorted, and a very large part of that is due to zoning restrictions. Zoning restrictions are severely constraining supply, and enabling those with capital to hoard property as an investment vehicle, rather than use it to buy a basic necessity. This scarcity allows landlords to keep a property empty rather than sell or rent at a lower rate, which would not be possible if buyers/renters had ample choice.
Not all rental properties are bought using a commercial loan, many are simply conventional loans where the owner decided to rent out their property rather than sell it. At least in the US, properties purchased with conventional loans can be rented out after the owner has lived in them after a few years. No commercial loan required.
The tax/accounting schemes you mentioned earlier would simply distort the market further without addressing the root problem: There's not enough housing for people that want it. Relaxing zoning rules would allow more housing to be built, and if there was enough of it, it would cease to be an "investment" rather than what they were built to be in the first place: Homes.
As a concrete example, I live in the SFBAY which has an extreme housing shortage. Yet my house is built on an unnecessarily big lot (required via zoning) and any structure built on it cannot be more than 27 feet tall. These are the kinds of rules that are severely distorting the market. I can't build a fourplex on the lot if I wanted to even if I have the space for it, and the demand is there. My next best option is to rent it out for way more than I otherwise could if there was a bunch more housing (Selling isn't really an option either because my mortgage rate is lower than what I could get in a HYSA; I'm basically being paid to borrow an appreciating asset).
All wholeheartedly agreed, but why shoot one arrow when you can shoot a whole quiver?
In addition to mandating upzoning (without allowing local municipalities to overrule or delay), increasing the cost of hoarding property without use would also help, by incentivizing selling or lowering rents.
And because it would be a punitive tax (primary good created simply by existing), there's no reason you couldn't roll the proceeds into programs to facilitate densification. E.g. tax credits for rebuilding existing properties with more units
So again, a disincentive to ever decrease rent (and thus demonstrate the market is softer and therefore you property is worth less).
Versus claiming it still commands higher rent (and is temporarily unrented) and thus more valuable.