Due to very shallow depth of field with f/2.0 and “less” at close range (example: Tisha Amstaff Sigma 30 @f/2 and close range);
In my opinion low light photography happens in aperture ranges down to 2.0. From there to wide open usable only for greater subject distances.
The low light capabilities truly should be covered quite well by an f/1.8 lens as the 35.
That leaves only the extra bokeh’ism as a plus (pro Sigma) for practical photography – not considering build quality.
A similar case: Reading reviews of 85/1.4 and 85/1.8 – comparing them, the initiated people never mention the aperture difference as a plus for LOW LIGHT photography (Note: Nikkor 85/1.4 is the classic “Cream machine” – nick-named so due to oustanding bokeh.
The Nikkor 85/1.8 is the cheaper version).