That's the problem with the lemming mentality on the forums. Everybody buys into the "moar power" that is necessary to drive a "real" car. Since it isn't their money, people are quick to say "just do it, it'll be fine".
The OP believed what the dealership told him. Combined with what he read here made him think "no problem" and made him forget the cardinal rule - if it isn't in writing then it doesn't exist. A dealer or tuning shop cannot change the terms and conditions of the factory warranty.
The OP learned an expensive lesson and is taking it out on the poor GTI - understandable but not fair to the car or to VW.
This is all the more interesting in light of a recent thread:
https://www.golfmk7.com/forums/showpost.php?p=642167&postcount=7
The OP believed what the dealership told him partly because if you come to forums like this you'll also hear people say ignorant things like "I went APR+ so I could keep my warranty intact".
But whenever someone calls out such ignorance, that person is as likely as not to be attacked for daring to point out the facts.
And that turns forums like this into nothing but a wasteland of what you describe as "lemming mentality" combined with sheer ignorance.