(I'll put this first so most of you all understand Eli's voice is not deep nor is it soft which adds more to the confusion)
Remember, Tabula Rasa lets him copy the concept of anything he smelts, not just its physical properties. So it's about what the thing fundamentally is or does, not just its appearance and can still use the abilitys like getting big if he smelts a celestial and he can only keep 12 at a time so if he already has 12 and wants to copy something else he has to let one go.
Eli is from 2017 before infinity-war and endgame so he doesn't know what comes after Guardians of the Galaxy vol 2
And don't expect him to get to multiversal to fast because that would break the story