I'm certain that there are at least five examples of this on every single toon in the game. It isn't necessarily done to "screw over the player" or simply to make you waste a piece of gear, it is done mostly for balancing reasons but also because of gear limitations.
Essentially as they keep increasing the gear threshold they need a way to balance out certain aspects of characters at various times and utilizing gear in that manner is a way to do it. Up until G12 finishers came out there wasn't a character specific way to do this, and instead was done by utilizing the limited gear in game. So yeah, actually giving GMY a G12 piece that instead gave him more special damage instead of physical might have made him OP.
A good example of this is when Jedi Revan came out the last gear level was G12+5 and that whole squad was absolutely OP. They were the hands-down meta, and the way they helped ease up their stranglehold on the top was with G12 finishers, which for all of the JKR meta team characters were quite lackluster. Suddenly with all things equal and characters at G13 General Grievous who got massive boosts from all G12 and up pieces was able to compete with JKR not only because he was boosted up but because JKR was given a lesser boost.
It's just something you have to live with.