It has HUGE blind spots in the firing arcs of those turrets. Enemy fighters could easily come in from anywhere to the rear side quadrants and hit the engines. Parking the forward turrets right in the shadow of those big beam cannons makes them vulnerable to a direct overhead attack.
A 'canard' style wing on the tip of the nose, sorta like a hammerhead shark, with a turret top and bottom on each side would clear their firing arcs. The other two turrets could be left right at the tip under the beam cannon muzzles and devoted to directly forward defense.
Ont the rear, leave four turrets, two top and two bottom, where they are for direct rear defense and move the rest out to the engine pods.
Anything you put in front of a turret to protect it is just something the turret can't protect! Examine where turrets were mounted on WW2 era bombers. Nose/chin, tip of the tail, middle of the top/dorsal side and often a ball turret smack in the middle of the bottom/ventral side, plus a waist gunner on each side behind the wings.
If it weren't for considerations of aerodynamics, weight etc, I bet they'd have parked a gun right behind each engine as those were primary targets for enemy fighters to take out to bring down a bomber.
On a bomber with a single tailfin, an ideal approach for a fighter was from the rear, slightly high and maybe just a bit to one side so the fin would block the dorsal turret, leaving the main danger the limited firing arc most of the tail gunners had. Twin tailfin bombers like the B-24 and B-25 had a clear field to the rear for the dorsal turret at the expense of having two shadows in the firing arc. A fighter coming in trhough one of those holes could find itself in danger from a waist gunner, but that was only a single gun VS the two most turrets had.
With the typical defensive arrangement, a bomber could engage up to six fighters. If seven or more came out to play... Bomber formations were designed so they could provide covering fire to one another while hopefully staying out of the way of each other's bullets. But losses were still extremely high until the long range P-51 Mustang fighter was developed that could escort bombers from takeoff all the way to their target and back home. (See especially the Tuskegee Airmen, who never lost a single bomber they were assigned to protect.)