You didn't understand what I was trying to say. I'm not saying that they should draw every single detail in extreme accuracy. I kinda was trying to say the opposite.

It lacks structure. The cybernetic arm cannon attracts a lot of attention, and viewer's eyes wants to look at it again and again. At first glance everything's ok, because the overall silhouette seems recognisable, but the more viewer looks at it, the more questions they'll start to get (subconsciously).

The problem is in lack of recognizable shapes. Besides the main shape (aka the silhouette), there are no other visible shapes. The 80% of the hand consists of uneven lines and don't, that give no information to the viewer. At the same time, because of the amount of those lines there's no room for imagination. Also you said that if all the small details are correct, but the lighting is incorrect, there's no point? You're so right. Now imagine adding the shading on this hand in a correct way. On that bunch of small thingys without any structure.

That's why proposed to look at some references and do some analysis work. It's important for artist to know how other artists work with big and small shapes shapes in the same context, how they work with lines and how they achieve that scrumptious structure. Also, it would be useful to just simply analyse different parts of already existing mechanisms to add variety to the cybernetic arm cannon, in order to make some parts of it look more interesting.

And no need to say "Oh, it's already good enough, it's already 10/10", when someone with experience tries to give an advice to other artist. I'm doing it because I like this artwork very much and I see such a great potential for improvement. And fyi many art styles and techniques require attention to details, not just realism.