Don't lots of manufactures make claims for neutrality and accuracy?
Anything from full size circumaural to iems, speakers etc.
But they all all sound different.
I love my ER4's but regardless of frequency graphs etc but they never struck me as sounding 'real'.
If you do take a close look at the response graphs they are close to the ideal
but don't match it.[what does?]
A few tweaks to the response [by way of passive filters] in these areas has for me resulted in a more even sounding phone for my own tastes.
Obviously iems interact slightly differently with individual ear canal shapes.
I also have Shure E4's [also tweaked
] and enjoy them too.
Since I Originally purchased the ER4 the iem market has exploded with many
more models to choose from, but for my purposes the ER4 is perfect.
[I even bought a spare pair]
The only time I can envisage looking for something different it when i decide
to go for a setup driven directly from the portable source without and external amp.[praying for that great ER4 isolation too
]
.