Questions about PVP

Quick question about PvP matchmaking when choosing your experience level for the first time.

Does the option you pick actually affect matchmaking long term? For example, if I choose the middle option, will I mainly get matched against other players who also picked that option?

Or is there some kind of hidden ELO/MMR system like in other competitive games that adjusts based on performance over time?

Basically, if the middle option ends up being too difficult, can I later shift down and get matched against newer/lower-skill players, or what is the initial choice of experience mostly for?