Both Sony A6600 and Fujifilm X-T2 have APS-C sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
One other difference between these two cameras that is worth mentioning is that Fujifilm X-T2's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the A6600 and X-T2 sensor size comparison.
Sony A6600 and Fujifilm X-T2 have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.