Were the Japanese "Kongo" class battlewagons advanced for their time?

@Jon Custer answered about actual characteristics of the cruiser. About the second part of your question:

Put another way, how much did the superior speed of the Kongos offset the greater heaviness of the Revenges and the King George V?

During WW2, there were many designs of heavy destroyers or heavy cruisers/battle cruisers that tried to outmatch heavier cruisers or battleships with speed and weaponry, even if they were inferior in armour and range.

Those designs had différent successes, manned by German, Japanese or French crews. Overall, the Royal Navy and the US Navy always managed to put a big battleship or a big cruiser in front of the fast ennemy boat, and to destroy or push back the ennemy. it depended of the tactical situation.

Since British and Japanese battlecruisers and battleships never met in a significant way, we can't really answer. However there are some points:

• Unless in night battle, a Kongo tasked to sink a King George V would have been a failure, but the Kongo would always have had an escape way
• When American battleships and Japanese battlecruisers met, the first often gained the upperhand, but they had either advantages: Two vs one, or radar and ambush situation.

The Kongo class battleships had one clear advantage over the British battleships. They were "upgradable," and actually upgraded around 1940. (The most nearly comparable British ships of the Lion class were scrapped in the 1920s.) In modern tech terms, the Kongos were "scalable." That made them "advanced" compared to ships built in 1910-1915, because they were already "modern" in the earlier period, and then "improved," based on the technologies of the late 1930s, of the King George V era. In World War II, the Japanese thus fielded ships that were "hybrids" between the earlier British battleships and the later King George V class.

It is noteworthy that the later improvements to the Kongos improved both speed (from 28 to 30 knots) and armor (by about 6,000 tons displacement), while keeping "guns" constant. Thus, the 1910s battle cruisers had advantages of speed over other British capital ships, but had advantages in armor and guns only over the Orion class. The later upgrades improved their armor to or beyond that of the Revenge class ships, leaving the latter superior only in gunnery. One commenter noted that the Kongo battle cruisers were "upgunned" Lions. But the later battleships had advantages of speed and armor over the Lions as well.

It is also striking that the British later "pulled back" the gun calibers of the King George V class to that of Kongos (14 inch), while giving them much more armor (even compared to the upgraded battleships), at a slight disadvantage in speed. Again, the advantage was in armor (in the late 1930s), but it was much more possible to have speedy ships that were heavily armored at that time than in 1910.

So at the risk of oversimplifying, speed, armor and gunnery represented "tradeoffs." The Kongos had the advantage of initially being designed as fast ships with competitive gunnery to potential opponents, at the sacrifice of armor. Later developments showed that it was probably easier to add armor than speed (decades later), meaning that the Japanese were successful in upgrading them.

If we stick to the time right around the completion of the Kongo class, we find they really are not that different from contemporary British battlecruisers. Yes, their appearance caused the USA to consider building battlecruisers, but that impulse did not start to be realized until after WW1 with the proposed Lexingtons, well out of the time frame to consider here. Realize that both battleships and battlecruisers were rapidly evolving, eventually converging on the fast battleships of WW2.

Let us compare two contemporaneous battlecruisers, the Japanese Kongo and the British Queen Mary, as built:

Kongo (specs listed as for Haruna, the last completed):

• Laid down 1/17/1911, commissioned 8/16/1913

• 27,384 tons, 704 feet long, 92 feet beam, 27 foot draft

• 64,000 shp, 27.5 knots

• 8x14” guns

• Armor: Belt – 3 to 8 inches, Deck 1 inch, Turrets 9-10 inches

Queen Mary:

• Laid down 3/6/1911, commissioned 9/4/1913

• 26,770 tons, 700’ 1” long, beam 89’ 1”, draft: 32’ 4”

• 75,000 shp, 28 knots

• 8x13.5” guns

• Armor: Belt – 4-9”, decks 2.5”, turrets: 9”

If anything, the slightly thicker armor and touch of speed of the Queen Mary makes it slightly better than the Kongo class.

Similarly, a comparison of contemporary British/American/Japanese battleships of that period (say King George V, Nevada, Fuso) also show close similarities with the Fuso having a bit less armor.

The extensive rebuilds of the Kongos between the wars only served to update the ships to be more like fast battleships than the battlecruisers they originally were. When push came to shove, neither Hiei or Kirishima could stand up to cruisers (Hiei) or new fast battleships (Kirishima).