And if an headphone sound only inside the head with an headphone feel instead of a speakers feeling outside or around the head it is unbalanced headphone for my ears...
Big +1 @mahgister It’s not only about balanced tonality but also imaging and soundstage. For me, if everything sounds like it’s inside my head it’s very limiting and not enjoyable, so overall “balance” can mean different things to different people, as always. But I have two pairs of Hifiman open-back ‘phones (HE400S and Arya Stealths) and find them to sound very neutral and balanced while also offering very good “out of the head” imaging/soundstage. Of course your choice of amp, DAC, cables, etc. will significantly influence whatever “balance” you ultimately achieve as well, so it’s obviously not just about the headphones. It’s the whole “the chain is only as strong as the weakest link” thing that’s pervasive and unavoidable throughout audio.