Sony A58 has a
20.0MP APS-C (23.2 x 15.4 m ) sized CMOS sensor . On the other hand, Fujifilm X-T20 has a
24.0MP APS-C (23.6 x 15.6 mm ) sized CMOS X-TRANS III sensor and features X-Processor Pro2 processor.
One other difference between these two cameras that is worth mentioning is that Fujifilm X-T20'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 moiré occurring in certain scenes.
Below you can see the A58 and X-T20 sensor size comparison.
Sony A58 and Fujifilm X-T20 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.