This reminds me of bolt gun v. semi-automatic. Bolt guns are generally more accurate because they have fewer moving parts than a semi-automatic. The fewer the number of moving parts, the more consistent the gun's harmonics. The less consistent the harmonics, the greater degree of variation in how the gun performs and this opens up the group.
Applied to fixed breech and hooked breech firearms, the fixed breech gun should be more accurate. How well fitted the hooked breech is and how much "slop" or movement depends on the how well assembled the gun is. For most of us, we probably don't shoot well enough to know the difference.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!