Overwatch is probably the most challenging in that list to properly port. Hearthstone isn't performance sensitive, frames per second and such doesn't matter, lag isn't an issue so long as it's not perceptible. In an FPS you're always slave to the clock, every millisecond counts, and the OpenGL support isn't there to squeeze what they need out of the mid-range GPUs.
Presumably this means Bizzard isn't interested in porting to Metal.
Last I heard, Blizzard ported World of Warcraft over to Metal with significant improvements. It wouldn't surprise me, though, if the relative age of the current Mac hardware is to blame.
Presumably this means Bizzard isn't interested in porting to Metal.