Hi ParanoiD,
From your WinMTR there looks to be around 20% packetloss here, which would indeed cause issues:
Keep in mind that different services will be impacted to different degrees due to this and for the voice chat example you mentioned this would show up very differently or not at all. You can read more about this in the Connection Troubleshooting FAQ.
Ultimately though if you’ve already expended the troubleshooting steps available to you, you’ll want to contact your service provider directly for further assistance.