> A landlord in Smith’s day is more or less the same as someone who buys a building and ...
Wealth of Nations is available for free online and Chapter 11 isn't that long [0]. You should probably find a copy and read it - he is talking about a different type of rent. He explains himself in excruciating detail and outlines how "rent" is controlling access to natural factors of production like kelp, timber, cropland (especially cropland, this is a major focus of his [1]), coal, hunting opportunities, yadda yadda.
If you want to grep for "After food, clothing and lodging are the two great wants of mankind." you can see he breaks down lodging into the natural elements used to create a house and how they all present opportunities for the person who controls the natural resource to extract rent. He isn't talking about renting out capital which is a significant part of what modern landlords do for tenants. Houses (and apartments) aren't naturally occurring.
> This is the thrust of his argument, the landlord is an immoral parasite because he “reaps what he does not sow,”
Smith, you and I all agree on that. But we agree in the context Smith was using the word where that was all the landlord was doing. In the modern context, you can take all the parasitic aspects out of the landlord and there'll still be something left behind that you pay money to every month. The house doesn't appear by almost-magic like coal does - someone has to build it and the owner doesn't have to be the same as the beneficial user.
[0] https://en.wikisource.org/wiki/The_Wealth_of_Nations/Book_I/... - let's use a better link than the Marxists
[1] We get this choice quote: "Food is, in this manner, not only the original source of rent, but every other part of the produce of land which afterward affords rent derives that part of its value from the improvement of the powers of labor in producing food by means of the improvement and cultivation of land."