As Aadil is my guruji I’d be more likely to follow his direction considering his study with Iyengar since childhood and the 40 years of asana in his own body.
However, he himself would tell you (I believe) that you may feel and explore this for yourself to determine its efficacy in your living. If he’s saying the foot is flexed he’s saying it not from his personal preference, his flavor of the day, or something he learned over the summer in Pune but rather what he has learned from an incredibly deep and robust practice.
In the pose you mention, for me in my body, pointing the back foot significantly reduces the energy in the lower leg. For me there is an equanimity of power in the back leg when the foot is flexed and that allows a spreading in the pose (three directions) which expands the heart center and moves light more efficiently across the palette of the body.
As for the fingers, they can be spread however this is usually for a student that is feeling a great deal of anxiety. So if that is you in the practice - be it now or in the future, then spreading the fingers will dissipate your anxiety. Otherwise the fingers are together so as not to fray the energetics of the pose as previously mentioned.
So there is no “should”. There are just different purposes for different students in different contexts. Unfortunately this can be muddied by the fact that becoming a “yoga teacher” can happen in a weekend when in fact it really cannot at all happen in a weekend.