The models and everything is in the client however. Which, 10 years ago, you could've purchased legally. That, under European law, entitles you to play the game as you feel free. Because TOC that are only visible after the purchase of a product do NOT apply under EU law.
On top of that, EU law is very specific about reverse engineering. Therefore if the server tells the client to display a certain model it already has, something that the user has legally obtained and is free to use, they cannot sue for copyright infringement.
However, you are right about the copyrighted ideas. That's plagiatism to an extent and they COULD sue for that.
Don't take any of that at face value. I'm no expert and have no law degree, I just have done a fair amount of reading over the years.