By saying there's nothing wrong with them meant that they were not structually suspect or faulty by design (although no ships perfect and the RN's BCs were by no means great ships). Their main faults was in ammo storage and handling which was a crew and officer done thing which lead to the explosions. The RN ships were not sunk by a direct hit on the magazine, and if it was, then there would be something wrong with them.
There were structural failures of the design, but these would have been hard to prevent in the build phase because you would need advance computers to fix the issues. And a lot of the issues were related to powder. And some related to handling. IMO, this is order of responsible items, high to low.
1) Cordite went boom, not whoosh like German. It has largely to do with some of the additives used. It is possible to find through heavy test, but it is also easy to understand how it could be missed. The tests needed to be done in a full scale, full quality turret to get the pressures and conditions right. AFAIK, building full BB turrets on test ranges to blow up for safety test of ammo was never done.
2) Post war, it was learned that the flash protection would not stop the flash even if in perfect condition and perfectly used on at least some class of ship. Again, to point 1. In retrospect it would have been wise to test a full turret for each class, but it was not a known issue at the time. A lot is the difference between more modern "full system testing" and "test the components, assume it works right as a system". And to be fair we can see many examples of this in modern time, where something is missed that is only discovered after it is built. (F-22 O2 system, Osprey issues).
3) The first two set the stage. The next item relates to the black powder bag that start the cordite explosion. The silk leaked black powder. Evidently, it was manageable when firing on test ranges under non-realistic conditions. The problem became that at the high rate of fire in battle, the powder started accumulating on doors and the floor forming a black powder explosion chain.
4) BC were not intended to be in main battle line when designed. If the Admirals had used say the QE as scouts, we likely are not having this discussion.
5) Yes, the pressure to raise firing rates and keep extra bags high in turret hurt. But it is not the main cause. It is key to understand that even if the textbook amount of powder was high in the turret, and one of them was ignited by a hit, in most cases the fire still gets to the main powder magazine. In combat, there will always be fresh bags on their way up. After all, if the gun fires every 15 to 30 seconds, we have fresh bags arriving in the upper turret every 20 seconds or so. One would have to look at the time from main powder magazine to closed breach to see how many would be in transit at any given time.
It is really an story of inferior powder combined with two structural issues (light armor on BC and too weak a flash protection) combined with an aggressive take chance attitude and an emphasis on rate of fire over safety protocols. Italian and German admirals are rightly criticized for being to cautious. But being highly aggressive also carries downside risks.