Over time this will bother you less and less. At first when I got my first good headphones (Philips SHP9600) I was like “woah, space!” and “woah, instrument separation” for about a month. You still hear this but your brain won’t be distracted as much as you get used to it. I’d say do your best to enjoy music with your new headphones, it will be counterintuitive to downgrade over something like this but if it does come to that I can’t blame you.

I wasn’t comparing them to a dongle. I use it for kicks to see how much a source matters for headphones. Not the best testing method though.

Yeah the HE400se can sound anemic for lack of a better term on a poor amplifier. What I use as a poor source to test a headphone is the 3.5mm output of my Xbox One X controller. The bass sounded a little strange and fell off very fast. 3/4 volume to be listenable. I do use them on my iFi Zen DAC via 4.4mm and it works wonders. I did try them on the unbalanced output but there’s barely any difference if I can even say, and it’s quieter compared to balanced but all that needs is more on the volume knob.