Comparing the XBone/PS4's GPU to a graphics card with similar main memory setup, CUs, clock and ROPs is just not really accurate. Of course, ESRAM ist not a game changer, but it certainly (and only to some extend) mitigates the overall performance disadvantage of XBone compared to a graphics card that has only DDR3 and nothing else.
The AMD cards I referenced both had GDDR5, even the Xbone equivalent.