It probably takes region into account, but its not the main criteria, because i mostly play with users from other regions.
The main criteria for matching you up with a player is probably your skill level, and your preference. And…i think your waiting time as well.
Evolve isnt in the top most played steam games list, so it has less than 2000 players online( at highest peak ). When i usually play, there are very few players online…probably less than 10-20, so i pretty much have to wait quite a while, and then get matched with same faces most of the time.
I think that ideally the search tries to match you with monsters with same rank as you, from same region as you, while also taking account your hunter role preference.
If you want to play as an assault, but get placed into a team where other players also prefer assault, it probably means there werent enough players online to make the “perfect” match, and it compromised. In that case…leaving and rejoining is unlikely to help.