Companions don't need to be some narrow conception of "normal". Companions can be special, they can be extra ordinary, they don't have to be a regular Joe Blogs from modern day Britain tired of working a 9-5 job. They can be space adventurers, alien scientist, penguins, even other Time Lords.
The primary role of a companion is to be the novice, the inexperienced individual who travels with the Doctor and ask right questions so the plot can function. That's it. Besides that, the companion can be anyone from anywhere.
The insistence that they all have to fit into this little box of what a "normal" audience surrogate is something that has been hurting the show for a while now, because it just keeps cycling through the same concept (dissatisfied young person from modern day Britain) again and again and again and...
