Technically they were post Dreadnought as they were completed after Dreadnought as resources were diverted to Dreadnought. The main benefit of Dreadnought was actually turbine propulsion which increased fleet speed and reliability.
The LN class were very powerful ships for their time and little inferior to the early Dreadnoughts particularly at closer ranges and therein lies the issue. When designed LN were to fight at relatively short range where their 9.2" guns were first rate armor piercing weapons. At long range their powers dropped off significantly and the mixed battery with different flight times became very problematical to control.
Dreadnought with a uniform 12" battery facilitated long range gunnery as you just need more shells to hit a target at long range. Uniform gun size also gave the same flight times of shells so were much easier to aim.
We tend to think of the old pre-dreadnoughts with their 6" secondary batteries as such but in reality in the 1899 time the 6" battery was considered to be part of the main armament to smother the enemy whilst the slower firing 12" guns finished them off. By LN and Dreadnought times the rate of fire of 12" guns had increases from one round every one to two mins to two rounds every min so there was a massive increase in actual firepower which again facilitated long range.
Longer range was also dictated by the invention of the heater unit in torpedo's and the gyroscope for accuracy so big ships had to stay outside effective torpedo range to fight, so again longer ranges came in. In fact the torpedo menace was vastly overestimated in real war situations. Battleships carried torpedo's as they were such a powerful weapon but (other than Nelson/Bismarck 1941 and that is disputed) no battleship ever torpedoed another battleship!!
A fascinating period in naval architecture.
Cheers
Geoff