I am not sure I would agree they are wildly different, although sure they do vary. But what you cannot get from graphs are perceptions like, it sounds "wider", or more "open". The thing is, if they varied so much, and changed over time so much, then you would typically end up with a scenario where both left and right drivers were very different and you would get a very muddled soundstage as instruments actually moved from left to right depending on the frequency.
Most all headphones are pretty stable in the upper bass, mid and lower treble. Changes tend to happen at the ends and there isn't really enough going on there for you to notice channel imbalance in a 'matched' pair. Especially true of planars since their imaging isn't very pinpoint compared to say an HD800.
And adjectives do very much fall on a freq resp graphs. You just need to know what ranges are responsible for what perceptions. When they aren't overblown you can absolutely have a deviation from neutral that delivers the sonic goal without drawing attention to itself. For example the LCD-3 by virtue of dropping upper mids and treble inversely boosts fullness, warmth, punch and rumble but recently also jacked up the upper treble to increase air. The HD800 goes a different route boosting the definition and warmth range. That boost to definition is what makes it picky to upstream gear since any grain, hardness, aggression or brightness is going to hurt. I've actually cancelled it out on my HD800 so that I keep the modest warmth bump but get linear treble performance.