Conventional wisdom has the deletion of the secondary amrmament as a primary reason for the construction of Dreadnought and all-big gun designs in general*. When they were added back on in later classes, it was in some senses a repudiation of one of the original ideas behind the all-big gun concept. Including secondary armament from the beginning would make Dreadnoughts just a scaling up of the pre-dreadnoughts, and less of a distinct concept. As a side note, the Germans and Japanese never really subscribed to the idea of stripping the secondary armament on all-big gun designs. Nassau had a fairly standard secondary armament upon construction, and Satsuma had a sort of middling ground.Well they did think that the wing turrets would be able fire straight forward, in practice this proved impossible due to blast damage. If they had realized this then the design could have deleted them ( maybe upgraded the remaining turrets to triples ). One issue with Dreadnought as built was that it had no secondary guns, this meant she was defenseless against torpedo boats. At the time it was decided she would always have a screen that would deal with them but later guns were added. Replacing the wing turrets with turreted twin secondaries would have helped.
*here I'm using all-big gun to refer to the whole set of designs which existed at the time and shared that as a unifying and defining trait. Dreadnought specifically has other additonal influences on its design so I'm refering to the general concept.