More probably this is routing issue. Connection between Deutsche Telekom and Youtube servers is more busy than connections between DT -> Swiss server -> Youtube.
To add, when you're asking DTAG to peer, they determine the location where they set up the peering point with you. That's typically somewhere out of nowhere, so you also have to rent the pipe that brings your data there - from them, obviously.
Additionally, they overcharge a lot for the last mile infrastructure for other ISPs, so in my region some other ISPs started building their own last mile infrastructure and peering with Telia to get access to TAT-14 (and thereby allowing them to peer better with US providers).
(TAT-14 is a transatlantic cable owned by DTAG and Telia)
It’s common knowledge in the industry by now that the DTAG uses their 40 million users as leverage to force companies to directly peer with them (and pay for peering).
ALL traffic from DTAG users first runs to a Level3 datacenter in New York, and from there goes to other users.
While all other German ISPs have a peering node at DECIX