If you had a proportional voting system, you'd probably get more parties. (Parties with a chance to get someone elected.)
I don't know if that's good or not. Germany uses a strange in-between system, and it also has a threshold, i.e. you need 5% of the votes (or alternatively win three districts) to get into parliament.
If you review that list, you'll note that where the rubber meets the ground (rules of operations) there is a huge body of governing rules that are extra-constitutional and developed over the course of the past couple of hundred years by the two establishment parties.
As an analogy, consider supplying independently developed applications for a platform with a proprietary OS where the OS vendor has a vested interest in keeping independents out (or ineffective).
And even before reaching the forum, the non establishment entities must dance to the tune orchestrated by (you guessed it) the establishment:
Its a chicken and egg problem. We need a Supreme Court that can review and strike down faulty laws enacted by the entrenched interests to revise the system. But to get to the Supreme Court, the candidate needs to be nominated by the establishment President and approved by the establishment Congress.
I don't know if that's good or not. Germany uses a strange in-between system, and it also has a threshold, i.e. you need 5% of the votes (or alternatively win three districts) to get into parliament.