Superfiring turrets did not actually fire directly over one another as a matter of course. Depending on the design of the turrets and especially the sighting devices, it ranged from outright impossible, and lethal for the crew of the lower turret, to merely extremely unpleasant and disruptive of their own shooting. Whenever possible, a pursuing fleet would follow a parallel but offset course to its quarry, or else turn away slightly to clear its firing arcs before resuming the direct stern chase. This was practiced for instance by American battleships pursuing the remnants of the Japanese fleet that escaped Operation Hailstone at Truk in 1944.

Even to he extent having more forward firing guns was desirable, no battleship or battlecruiser ever had more than two primary turrets superfiring. Given that, more than six forward-firing guns (which was what you got in the common 2x3 fore, 1x3 aft arrangement) was not possible without adopting the quadruple turret. Quad turrets, of course, brought with them other problems. There was the increased risk of losing four guns to a single hit, which actually happened to Jean Bart at Casablanca, and the British had well-known problems with rate of fire from their quads.

The advantage the all-forward arrangement had that actually drove the design of the Nelson class and similar French ships was that it reduced the length of ship that required heavy armor. By do so it allowed the same weight of armor to provide thicker protection (or equivalent protection for less weight). It's very significant that the only classes of all-forward capital ship were designed against strict tonnage limitations.