Am I missing something here or EQ on master is some kind of "wrong mix fix" for people that doesn´t have access to the individual tracks of the mix?
In the way you're describing it -- eq-ing to change the spectral balance of the mix -- yes, you've heard this yourself and I can confirm you're not hallucinating.
Why then do mastering suites inevitably include some eq?
For musical styles where every song has different instruments and perhaps mixed by different people (some electronica, industrial, pop albums, etc), mastering eq is usually necessary to keep the overall sound reasonably consistent from one track to the next. If you work with nothing but metal, it's easy to forget that other types of music have different demands but mastering studios have to deal with all kinds of client material, and most of the "tips & tricks" pages you'll find on the web aren't written with metal in mind.
On a metal album usually the core instruments (rhythm gtr, bassguitar, drums, lead vocal) are the same sounds in all tracks, so that consistency is normally there anyway. In that case master eq is only necessary for compensating for lack of flatness in the monitor setup used in mixing - or "bad" decisions made by the mix engineer. And mastering engineers, as you say, do not normally have access to the individual tracks.
It may also be necessary to eq to compensate for tonal changes caused by the other fx in the 2-buss chain - like Abyss of Dreams says about compression losing some highs. That's a different issue to what you're describing, 'cos in this case you're eq-ing to
maintain the spectral balance of the mix rather than to change it. If you're mixing and mastering simultaneously, you can eq the individual tracks to pre-compensate for 2-buss compression, but this will change the response of the compressor to the mix, perhaps audibly and perhaps not beneficially. That depends on the particular mix and the sound you're going for of course - sometimes post-compression eq will be the perferred solution.
