Slowplayers are a reality. Threads/reports about them can be found here
Im not sure if you (refugee/aim4whirledpeas) knew that, at least your postings seem to suggest that this behaviour is new to you.
The fundamental problem in dealing with them is that accounts
are easy to ban, but banning players
is hard, they just make a new account. That is not speculation, that has happened several times, and apparently repeatedly by the same person(s).
Doing a general IP ban is problematic, it can affect people not involved (think WLAN hotspot at a university).
The proposed method to handle this is to resign if you detect this, and blacklist that account (click the lightning bolt icon at the end-of-game screen). If you want to blacklist an account later, just click the "Friend List" tab at the top of the screen, click on the "Blacklist" button, enter the account name in the edit box at the bottom of the screen and click "Add".
That means you will not be matched against that account in the future. You will take a ratings loss for the resign. If/when that account is later banned, the ratings loss will be gone. But the main idea is to minimize the influence that toxic account has on your game experience.
Some players, maybe many, disagree with that approach, and want something more to be done against those accounts. As I tried to explain, it's hard to reach beyond the account to the player behind it.