Graham, a few points of detail:
RSM, as you will recall, was not a rank, but an appointment. It became necessary to change the title of the appointment of the senior soldier in the battalion from 'Sergeant Major' as soon as Company Sergeant Majors were appointed. This was first described in AO323/1913 October ...... "these duties [CSM and CQMS] will be carried out by the existing Colour Sergeants".
No longer could the senior soldier be the SM, with four other SMs about [who were at that time two ranks junior to him, with all [R]QMSs in between].
The new CSMs retained their SD rank badge of three chevrons and crown [see CSM Barter VC, always badged thus] [i have no evidence that Colour Sergeants changed the size of the crown when appointed CSM, and can see no good reason for it in time of war] until order was restored and a second grade of Warrant Officer was created [AOs 70, 168 and 174 of 1915]. Until then, a RSM wore the crown, a RQMS continued with four chevrons and star, a QMS not appointed as RQMS just the chevrons, and a CQMS as CSgt badges.
With the creation of WO II, CSgts appointed CSM took the crown, and WO I appointed RSM took the Royal Arms. The poor old QMSs were lumped in with the CSMs [they had hitherto been their seniors] and were to wear the crown also.
Finally, AO 309 of 1918 gave the RQMS WO II back his dignity of a new usage of the crown within a wreath, thus showing the senior appointment.