what will you play on the pvp tlp?

I think there's just a large lack of understanding of how Intellectual Property Laws work. Unfortunately if you don't understand you're probably not going to.

I understand it perfectly. There is no law stating you cannot use the game client to connect to a non-official server. If you believe otherwise, prove it.

It's the setting up the server that is the issue.
https://www.copyright.gov/help/faq/faq-fairuse.html

You are not allowed legally to use the entire lore/quests/spells/setting/art files/etc from a commerical product to setup your own competing version. Even if yours is free and only has a dozen users, its still potential losses for DBG.

You don't get it. Their work isn't being used at all by private server developers.
Let me explain the 4 parts of an MMO again:
-The client software, this is what is on your computer
-The server software, this is the code that makes the game function
-The server hardware, the physical computer the server software is hosted on and the location the client softwares connects to
-The database, technically a part of the server software, it stores values and information, things like player HP and location, quest progress, how much magic resist a mob has, respawn timers

Private server developers produce their own server software and database, and purchase their own server hardware.

Private server developers don't have to touch the client at all. The client is on the player's computer. The player isn't infringing copyright by connecting to a non-official server, and the devs aren't as long as they aren't sending the client to anyone.

While you are playing an online game, the client is not being shared to or from anywhere. Data called packets are sent back and forth between the client and server, the server tells the client what should be happening on the screen and the client relays that to the display. Packets are just commands and instructions and numerical values, not copyrighted data, and even if it were, it would be something a private server dev created themselves.

Edit: The devs are not using the client. The players are, and as long as they obtained their copy of the game legally, they aren't breaking any laws.

So are you suggesting that all the quest dialog , lore information, item names/stats for every single quest, item, armor etc are all stored locally and the server just tells it to read it to you? Or are you suggesting that servers somehow don't use quests and items from the actual game? Because otherwise I'm not sure how you think they're not serving/using DBG's intellectual property to whoever is playing on these servers.

From a pvp that has no support to what constitutes copyright infringement.

While Atmos has a good case in his above statement;

If your private server grows extremely popular and (x) company thinks you are doing them harm they'll simply do a analysis against pursuing you in a court on resources vs. resources. Any decent legal firm will then tell the defendant that the cost to defend will start around (x) do you want to defend even if you win.

It depends on the company and the industry. I worked for a company that spent $6 million fighting a patent infringement case. The inventor only wanted $2 million in royalties. For whatever reason, the company decided to fight it rather than pay it. Some of you are thinking, "Boy, that's really dumb" but there is always more to it than meets the eye. In this case, the were convinced they didn't infringe and stood their ground.

The inventor died before he collected but his family took up the suit. That was 10+ years ago so I don't know where it ended. In retrospect, the whole affair was lose/lose.