Going by the graph in the article, that's still ~13% of homes owned by investors with >5 properties. And that's total of what is currently held, it speaks nothing of liquidity. That number likely includes investors who have had that property for a long time, the current property buy-up likely means far greater than 13% of the market right now is going to those sorts of aggregators.
Dropping the price of a house by a few percentage points can be the make-or-break for some families. And small changes in availability can have large impacts on price.
If we banned (or severely penalized) all entities from owning more than 5 residential homes, this would probably reduce cost by a few percentage points across the board. That's thousands of dollars.
Personally, I think unoccupied homes in general ought to be penalized (beyond just tax burden, an actual vacancy tax).
>Personally, I think unoccupied homes in general ought to be penalized
As is done in the UK
I think Vancouver has a vacancy tax. Does it work?
You may be interested in learning about the Land Value Tax[0] which will in effect, taxes become more burdensome for leaving land unproductive (e.g., empty housing or land). It also shifts the calculus on home improvements, which means remodeling your home or doing other perhaps large pieces of upkeep will not trigger a property tax increase as it does today, which is better for median home owners as well.
[0]: https://en.wikipedia.org/wiki/Land_value_tax