Which is hardly the common case for an individual piece of real estate. You don't even need perfect substitutes as long as the substitutes are close enough to prevent monopoly pricing.
> This is often the case with real property, and also with much intellectual property.
"Intellectual property" isn't normal property. It is a monopoly in the lack of competition sense. This is especially true for patents which much more rarely have good substitutes (since the same patent is written to cover them too), but is often the case with copyright as well, as with Microsoft. "Intellectual property" is basically worthless if there are many perfect substitutes because it's non-rivalrous. With real property increasing market share inherently requires increasing capital expenditures. A landlord willing to engage in aggressive price competition can't instantly saturate the market by providing 10,000 units to 10,000 tenants when they only own 10. If LibreOffice was a perfect substitute for MS Office then they could do exactly that.
This is why in markets like movies and music where there is good substitution possible, the markets tend toward cartels, because otherwise they would be extremely low margin commodity markets. Which is why those companies hate the internet -- it's interfering with their ability to hold the cartel together by reducing their control over distribution channels.
That's just equivocating two meanings of the same word though. A title to real estate is a "monopoly" over a piece of land, but it isn't inherently a "monopoly" in the sense that you have no competitors. If you own an apartment building but someone else owns a similar one across the street from you, you have competition. You don't own every apartment building. And it's only in the second sense that a monopoly would be problematic.