This is getting a bit off-topic, but you’ll notice the issue once you try a Waldorf Blofeld or a MicroMonsta2 in the studio with USB. But if you use a grounded mixer in between you’ll hardly ever notice it.
The laptop issue is indeed a thing. If you power an audio interface through an ungrounded laptop, the audio output to the mixer/speakers becomes the ground for the laptop.
I’ve also seen it the other way around a lot, cutting the ground to the laptop solves it. That’s why it’s always handy to have an extension cord with ungrounded outlets in a live setting.
I agree both option is best, like the SP-404MKII. I still hate USB-C though and the fact that there’s not a more durable connector with the same capabilities. The USB-B connector for USB 3.x is an abomination.
Continue to post the observation posts that didn’t seem to connect with the OPs plight about all aspects of the DT II over on the existing news topic on it