Earlier quoted context omitted.
"Basic rules of fairness" is meaningless crap that roughly translates to, "we aren't as good so we will keep passing regulations in favor of locals until it's insane for anyone else to try." Frankly, it wouldn't be that surprising if net neutrality started getting violated in Europe by protectionism laws.
I have family in Germany who get their internet through Deutsche Telekom. When visiting I've found its faster to watch YouTube via a VPN through Switzerland than directly through Deutsche Telekom. While this doesn't prove anything it sure does feel like they already violate net neutrality when it comes to YouTube
As for the issue at hand (YT being slow), like a sibling post states, that's because they refuse to peer at DECIX where everybody else is. They even tried to frame the NSA scandals as "IT companies, be responsible, keep user data in German networks and peer with us directly (on our terms, which will be expensive for you - they 'forgot' to mention that in the press releases)".
The best way to make DTAG more customer friendly (both upstream and downstream) is to move somewhere else.
Luckily in cities you have 5+ ISPs to choose from (some of them DTAG resellers, but still an improvement), and even on the country side it's typically at least 3.