In this article, the authors (Amir Siraj & Abraham Loeb) estimate there should be 5-10 Earth-sized planets in interstellar space for every star.

The reasoning is based on inferred numbers of interstellar objects based on the observation of I/`Oumuamua and 2I/Borisov.

Is this a bit shaky, and has not the space density of rogue planets been constrained to be lower than this by lensing searches?

Preliminary Evidence That Protoplanetary Disks Eject More Mass Than They Retain