I do use EQ, but only really to add a bass shelf to taste, or minor tweaks at the top end (DT1990 with fresh pads needs a small cut at 8Khz, with worn in pads it's fine).

I don't use presets because I've realised that they tend to destroy any unique character of the headphones, or that a preset created to someone else's preference most likely doesn't match mine.

The headphones that I actually use already have a frequency response that appeals to me, they don't need a major overhaul. I don't see much sense in starting with a headphone that you think sounds like shit and then digitally reworking every part of the frequency range until its acceptable. The possible exception to this might be if something offers an experience that nothing else can replicate, for example audeze's large diaphragm planar IEMs. Nothing else offers a true open back IEM experience, so if that's what you want, then EQing your way around the shitty tuning might be worthwhile.