Sorry for just dropping the video earlier and dipping, I was at work but really wanted to chip in on this topic.

Ok so first, it's good to have an idea how we hear and what the driver is doing in regard to pressure waves when generating sound. https://imgur.com/a/AYU9ciU So in this image it depicts individual frequency waves and then they are combined in an analog signal for the driver to create them, they are all added (and subtracted) together into a single waveform that the driver follows. That creates the pressure waves that our ears pick up and extract information from. Now when applying that to frequency response, the varying SPL of differing frequencies has a direct affect on the shape of the waveform due to differing amplitude in various frequencies.

With that in mind it's also good to know about things like auditory masking. When multiple close together frequencies are played, if one is substantially louder than other similar frequencies being played, our brain filters the quieter ones out. The range of frequencies masked is dependent on how loud the peak is. So with headphones that have substantial variation in it's FR, it may sound either more "detailed" or less "detailed" than another based on it's FR. Personally I believe this is also one of the factors that causes the perception of "fast or slow" headphones, despite their drivers not actually responding in a "fast or slow manner" (in the sense its often described).

That said, it's not discounting headphones, different drivers, and the research or quality put into them. Different headphones and drivers may have their own unique frequency response due to various factors, and EQing is more like bending that overall tonality, but specifical characteristics of the FR that may make them sound unique will still be present.

So no you can't just look at a graph and know exactly how it will sound, or use a FR graph to EQ it perfectly to you because of differences in transfer function and acoustic impedance. Even if they measure the same on a graph, it may differ at your eardrum.

To summarize, FR at your eardrum in theory contains all the information you need, but actually extracting that information from FR is not reliable and FR made on standardized rigs is better used as a tool, but still trust your ears first