I have aways understood this remark to reflect the degree to which the RN learnt the lessons by the end of the war: RN flash protection was vastely better by then (and had to be due to the less stable propellant) than the HSF, which was just about good enough for the more stable Ge propellantOK.
1) Do you take into account the different vulnerabilities of British and German cordite (at the time of Jutland) to flash? and if so, how? As far as I recall at the end of the war when the British inspected the High Seas fleet they do not consider their gunhouses 'flash tight' - but it was not the German ships that were blowing up at Jutland
Certainly the end of 1918 does not give a RN datum for 1916!