Pokémon GO
You next to your XXL, from a screenshot.
Pokémon GO already prints name, height, and weight on the Pokémon screen. Height Lineup reads that screenshot on your device and places the Pokémon on the same chart as you.
The importer is a beta. It uses on-device text recognition. PokéAPI is contacted only for a public name index or artwork. The screenshot itself is not uploaded to Height Lineup.
That is the useful comparison: not one Pokémon against another Pokémon, but your own height against the XXS or XXL you actually caught.