do designers' skills make good designers?

It has been oft-stated, by myself and others, that one reason that Engineers make poor designers of software (from a usability perspective) is that they are too high-functioning. That is, by definition Engineers are far more intelligent than the average human, and have studied, learned, and taken into their mental practices highly abstract and complex concepts such as 'symbolic substitution', 'hierarchies', 'object orientation' and 'inheritance', the 'in-memory-vs-on-disk' disparity, etc.

Consider 'symbolic substitution'. This is the use of a 'variable', or letter or word, say 'a', or 'mySalary' to stand in for, or substitute for, an actual value during a calculation. This is the basis of Algebra, but how many adult humans are comfortable with Algebra? How many fear and loathe the subject?

One definition of a UI Designer, if one is to judge by job postings for them, is their proficiency in hard-to-use techniques and tools, notably in the use of Photoshop and Illustrator and Flash, and in the ability to draw. A good designer has taken into his/her mental practices many arcane and bizzare constructs such a layers, outlines, timelines, perspective, anti-aliasing, etc.

Wouldn't you think people who use and are proficient in easy things would do a better job of designing things to be easy? Just as Engineers' use of complex tools such as Object Oriented Programming Languages contaminates their brains and makes them think at too high a level, wouldn't Designers' use of complex tools such as Photoshop contaminate their ability to design simple interactions?