Cable TV internet is horribly oversold - Kabel Deutschland was already infamous, when they got bought up by Vodafone shit got even worse. DSL ... let's just say most of Germany is happy to have 16/1 ADSL. I have 100/10 FTTB via M-net and even they have load problems.
Cellphone internet is even worse but as data is horribly expensive in Germany no one dares streaming Netflix over that anyway...
tl;dr: it's not Netflix fault, it's last mile telcos who have done jack shit the last decade to build out new FTTP infra coupled with appropriate uplink capacity to the nearest IX, but people are too dumb to understand this and blame Netflix instead of directing their anger towards politicians and telcos where it belongs!
Luckily we have net-neutrality infringing features like Telekom's "Stream On" where it's included /s