I find eq'ing mostly effects slower drivers like dynamics. For faster drivers like planar's, I find the technical performance isn't effected nearly as much because it can account for more demanding loads. If you, for example, boost the midbass on a DD too much, it can run into issues with mud due to how much more air it has to push, lowering the precision of higher frequency notes. That being said, eq'ing too much of anything can present quality issues, it mostly depends on how much eq you're applying.