I love it when people compare stance dancing they always seems to forget that the effect is also completely different.
Using shield oath or grit gives you a self sustained 20%damage reduction directly. Using defiance gives you absolutely nothing on your own and that actually makes a huge difference also. You need to be baby sitted by a healer to make turning defiance worth

The CD is also way longer a full 10 secs for warrior.
Maybe stance dance looks more appealing but it also has some major downside as well