I wrote a bit about this topic here. To summarise, an all-forward turret layout requires compromising on damaged stability - a shorter length of the waterline is protected compared to a more conventional design, so flooding of the unarmoured part can cause a dangerous loss of stability that a conventional design would not suffer from. The all-forward design also makes placing AA armament more difficult. An ideal placement for them would be around a midships citadel, something only achievable with a more conventional design.