So I think a few things are going on here.

1. The dt 770s are made for audio production where you want to hear everything, good bad and the ugly. So when paired with a source that may not be geared towards sounding great in all things but great in a few you'll definitely hear that.

2. A lot of people in this hobby don't like closed back headphones as they feel it sounds like the music and what not are being played through a clamshell. If he happens to have a pair of open back headphones give them a try and see what you think.

3. It may also be you're used to your Logitechs sound signature and that anything else sounds really weird. I have like six pairs of different headphones and when I switch between them it takes me a couple minutes to get used to how they sound.

4. And finally sound a subjective what sounds good to your friend doesn't necessarily mean it'll sound good to you. And a lot of people forget that in this hobby. So if you like the sound of your logitechs by all means enjoy them, because there is really no wrong way to enjoy audio even when there's those people out that that will tell you as such.