Your logic is flawed. One refers to a specific number, which is unique. Inhabited worlds is a category, which implies that if there were an infinite number of worlds, there would also be an infinite number of inhabited worlds, but their number would be relative to that of the uninhabited worlds.
For example:
For every one inhabited world, there are three uninhabited ones:
if y is the number of inhabited worlds, and x is the number of uninhabited ones, then;
y=x/3
If x=300, then y=100
If x is infinity, then y is one-third infinity. This can also be turned into a system of equations:
z is the total number of worlds
z=y+x
y=x/3
x=z/4
Why is x equal to z divided by four? Because if the universe is three parts uninhabited to one part inhabited, then it is made up of four parts, of which the inhabited part is one.
-Penguin