Actually it wasn't just the design of the british ships and propellants, but also their shipboard storage of ammo and the propellants. The admiralty manuals all said that ammo and propellant should be stored in the proper places, but the crews had ammo and propellant stored just about everywhere there was space. That was due to the british idea of being able to make up for a weaker targetting system by lobbing more shells at the enemy.
IIRC the problem was the propellant being so highly unstable that a hit in the magazine would touch it off, plus the admiralty rules regarding the opening and closing of the magazine doors, storage of shells and propellant were disregarded in the interests of faster gunnery. Items called flash guards (which completely sealed the doors in the barbettes) were also removed, again contrary to regulation, plus the British attitude toward warfare was, shall we say, uneven.
I am not sure whether I agree with you when you say propellant and ammo was stored everywhere there was space. It sounds like you're talking about the Hood disaster, which many think was caused by stowing highly explosive UP (rocket) ammunition on deck. This is unlikely to have been the cause of that disaster, nor those of Invincible, Inflexible and Queen Mary.
What probably did it were direct plunging fire hits to the Turrets or Barbettes, lighting off unstable cordite that was perhaps in quantities greater than it should have been. But I think the instability of the propellant was more to blame than the disregarding of the rules. The Germans probably broke a few as well, yet despite being holed, and holed and holed, Derfflinger, von der Tann, and Moltke survived. IMO the major difference was the Cordite.
The British gunnery 'system' was not inferior by the way. Though it is true the accuracy of British gun crews was very uneven, and Zeiss range finders were highly superior to British range finders, the British had a tremendous advantage in gun laying. Director Firing. The Germans fired their guns gun by gun. The British fired their broadside on the command of the director, all at once. This system was highly superior, and accounted for the British accuracy actually improving from the beginning of the battle to the end... Whereas the Germans had very good accuracy initially, but rather poor accuracy towards the end.
Regardless many British shells though they hit exploded upon impact, or failed to explode. The German shells, though compared to WWII shells or modern shells were pretty awful, still were vastly superior to the British shells. i.e. They pierced armour and exploded.
This is largely due to a difference in testing. The British did not do a lot of gunnery tests against armour. They did do a bit of gunnery practice, but not again against armour. Against target boats.
Krupp tested their guns in every concievable way and their shell designs were the product of that testing. They had firing ranges attended by the Kaiser and the General Staff who took the display of every new gun seriously. The Germans took gunnery seriously as a whole, unlike than the British, who though individual commanders like Roger Keyes and Percy Scott might value gunnery in an obsessive way, they didn't have the resources of a Krupp.