Dwarves are not small in the first place anyway. Small races are below 1,20m tall. Dwarves are around 1,30-1,50m tall. They are short, but not small.
In comparison, humans are only 10-30cm taller on average with their 1,60-1,80m heights.

They may appear smaller because they are stockier and wider. So unless you see them next to a human, you won’t realize they are only about a head or so sorter.

Discworld dwarves are something else.

Aluminum is cheaper to recycle than to make, even more so than glass.

It’s a simplistic statement, but it’s not meant to be that broad, it’s meant to be taken for this type of practice.

If everyone lived off leeching off someone else or from being middlemen, without producing anything, there would only be money moved with no products, labor, or services.

It’s not meant to be applied to something like “what if everyone’s business was just opening a pub?”. The economy would be destroyed without diversification and many kinds of businesses. But being a landlord isn’t anything like that. Particularly those that won’t freaking repair anything wrong with the house, just take their checks and the tenant is on their own.

If it would destroy the economy if everyone did it, then it should not be doable in the first place.