Mathematically it has to be that far off. Easy to see if it is the dovetail slot canted or sight bent if you put the rifle in a cradle and sight down the barrel from the muzzle end from a few feet away.
Thing is, if the top of the blade is off-center with the vertical barrel center line, your windage would be off significantly....and when you correct the windage with either front or rear sight it should shoot on target and windage will be consistent at any range. What you are attributing to a canted front sight is not physically possible unless the bullets are veering off of the longitudinal bore centerline when they depart the muzzle.
I have an NEF .45 Colt carbine that produces a severe corkscrew line of flight with any bullet or load, I forget exactly the pattern but it walks around the clock from 25, 50, 75, and 100 yards. Sighted in at 100 with a scope, it is something like 4-5" LOW and left or right (left I think) at 75.
Also remember that it takes about 5,000 caliber lengths of distance for a bullet to fully stabilize, and in that distance it can wobble and yaw all over the place.