To answer all of your questions, new strategies. People have improved from 2006 to 2019. Just because you are completely oblivious to new strategies doesn’t mean that they don’t exist. Join a hardcore guild or watch some youtube videos to see what strategies some guilds have made public.
As for the “authenticity” of private servers, no-one is arguing that the boss encounters are perfect. It seems that you are using that as a scapegoat argument to make the claim that private servers are very inaccurate and much easier. That isn’t the case. On average, they are overtuned from the original mechanics, as they go with the highest estimate for the additional challenge.