Do you people honestly think they would introduce these creatures without letting you use them in some capacity?

The entire point of Pokemon as an RPG is that you can recruit any type of enemy you fight, including bosses (legendaries). The "Pokemon" or "Ultra Beast" classifications are completely arbitrary. If you don't catch them the conventional way, you will use them some other way.
That's how these games work.
You are delusional and falling for the marketing if you think otherwise.