Why an eight-inch cruiser gun beats a comparable 7.5-inch weapon

Does a 7.5-inch gun's rate of fire make it better than an equivalent eight-inch gun?

No; their rates are too similar, so the eight-inch shell offers more effect without a meaningful handling penalty.

With similar mechanization, a 7.5-inch gun and an eight-inch gun achieve nearly the same rate of fire. The small caliber reduction therefore gives too little loading advantage to offset the eight-inch weapon's heavier shell. Six inches remains important because its ammunition is still light enough for efficient manual handling. At the other end, 9.2 inches becomes attractive when a navy wants a genuinely heavier cruiser weapon rather than an intermediate caliber with no clear payoff.