Yes.
But let me make the point that it's not even necessarily about subjective preference. There are real objective physiological differences between people's heads, ears, hearing that a personally calibrated EQ can, well... equalize. You can test that by comparing in-ear measurements with dummy head/coupler measurements.
Preferences are added on top of that, though it is hard to separate the objective from the subjective without experience or a neutral reference.
And this is probably where people new to equalization go wrong.
Let me draw an analogy: EQ is like the thermal compound between the CPU and the cooler. Both parts are designed to have smooth, flat surfaces (which cannot be said for most headphones and humans
) but the paste still has to even out all the surface irregularities including those that are completely unique to those parts. Even if the layer is very thin, without it the CPU temperature will be high and performance will suffer.