Big Sniper seeing through walls is actually a relatively new addition, because it was too easy to cheese the pre-fight before - there are two different colors in the vision (orange and red), and the red area can see through walls (think of it as short-range scanners vs long-range scanners)
As for the rest of the fight, it's definitely harder than big dog but it's not that far out from the natural difficulty curve, at least according to the testers. Just make sure to clear out as many enemies as you can before fighting him. Thanks for playing the mod, though!