Haven't you read the linked materials I posted and the other facts posted about the Rodney? If you are interested in learning something you might try this. These, along with the earlier the issues you raise.
The simple answer is that Rodney was able to hit the Bismarck because Bismarck was moving at 7 knots, the Bismarck could not maneuver, and the Rodney was firing at a range of less than 4000 yards for much of the battle. The RN gunnery apparently was not good. Tovey has been reported to have complained he would have a better chance hitting the Bismarck by throwing his binoculars than he would with the guns of KG V. From what I can I find, almost 2900 shells (2876 shells of all calibers by one count) were fired at the Bismarck by the KG V, the Rodney and the 2 cruisers, with around 300 to 400 shell estimated to have hit. Understandably, this is not considered exemplary gunnery.
Anyway, theNelRod guns had a dispersion problem even when the adjacent guns were not fired simultaneously because the guns wore so fast and used mismatched liners. The guns were no real improvement over the older 15" in range and were worse in accuracy per Worth. This would go to explaining the shooting at the Bismark.
As to the weight savings being a contributing factor to blast damage, this is a bit of a red herring. Consider this: only one capital ship, the Hood, had a greater displacement than the NelRods in the 1920s. The NelRods displaced more the Musashi and Nagoto in their original trim (eta: according to some sources--there seems to be a difference among sources as to this) and more than the Colorados. This suggests that blast damage problem was more than a cause due to weight savings--it suggests that it was due to a mediocre design of ship and weapon. For whatever the reason the NelRods suffered from blast damage that does not lessen the fact that blast damage was a problem.
Again, experts such as Worth describe the ship as less than successful. I realize that such a conclusion is unappealing to the fans of the Royal Navy, but that does not make the conclusion incorrect. The facts support it. I suggest rather than arguing with me using emotional statements, you use facts to rebut the conclusions I am reporting. Facts supporting your claims are far more impressive than illogical appeals to emotion.
I also must note, despite your attempt to label me as such, I am not a fan of the Bismarck. I noted earlier in this discussion that the Bismarck was also consider a poor design by such experts as Preston and Worth. To reiterate what I had he armor scheme was bad, the engines temperamental, the guns indifferent, and the platform unsteady.
Really, as Worth notes in Fleets of WW II, the real issue is that the Royal Navy did not design and build a truly successful capital ship after the superb Queen Elizabeths in World War. The Nelsons and KG Vs both had major issues.
There are numerous reasons for the RN's decline in capital ship design. These included such reasons as economics (the UK was broke after WW I), institutional arrogance (the RN thought they were better at designing warships than everyone else and did not realize the advances others made according to sources such as
The Royal Navy and Nazi Germany, 1933-1939: a study in appeasement and the origins of the Second World War), and politics (pick your political reason). As a result, the US and the Japan surpassed the UK.
If Rodney was as bad as you say how on earth did she manage to hit Bismark so hard at such ranges.
Blast damage well everyone knows the Nelrods were built too light to get under the Washington limit plus the effect of 3 closely grouped mounts magnified the damage. Big deal she sank a big modern battleship a few months in dry dock getting new light bulbs fitted is worth the effort (sarcasm for effect)
Dispersion only caused problems if all 3 guns in a mount were fired at once something which didnt happen very often.
Mount problems yes you keep going on about how bad it was in the early
1930s
Lightweight shells they still weighed a ton

yes they should have been heavier and a heavier shell was designed just the Royal Navy didnt have the money and had other things on its mind at the time and never got round to it.
Manouvering problems yes they had manouvering problems at low speeds such as entering harbour the rest of the time big deal theres lots of elbow room in the Atlantic.
For an old odd ship desperately in need of a refit she didnt do so bad did she. Not my favourite battle wagons I have always thought they would have looked okay when they finished building them.
The Bismark brigade always seem to forget there vunderschiffe was sunk by the cumulative effects of 1 ancient battlecruiser which desperately needed modernisation and had a glass chin, 1 brand new battleship which should still have been in the fitting out basin, 1 old battleship in need of a refit, 1 new battleship which had main armament problems and a Biplane.