I'd suggest making executions auto-performed, with the automation tied to the "elaborate executions - off" option in the "gameplay" section of the menu.
1. There's no actual point in manual executions, while mowing down the masses. While some may argue, that auto-executions may take up valuable time, the animation timing is much less, then, say knockdown recovery.
2. The manual execution technique is still somewhat sluggish. Even when streamlined by assigning the Middle Mouse Button.
3. Those not using the artistic representation of the executions would appreciate this logical solution. It's just like auto-loot collecting.