I feel the exact opposite... I love playing a pure cause I need to switch spec to fill niche meaning I experience different playstyle depending on fight or content within my same classe. I also love that I can be ultra versatile because of those 3 spec having different strength and weaknesses and different talent choice within themselves. I don't want to tank or heal so i could not be more happy to have all those avenue to explore within one classes. There is always something to learn or improve, something I don't think I could have with playing ww monk or ret pally.
I agree that the legendary system is not favorable spec switch this expention but even there I've been able to play all 3 spec to good level now that I have 2 shared legendary ( ring and belt).