Things like this can be very arbitrary from congregation to congregation and CO to CO.
Ugh! service overseer, secretary, WT study conductor, school conductor, ... I cant say that any of them were very good at handling their positions in the congregations I was in. The only time positions were changed were (1) when someone moved, removed, or died, (2) someone else actually wanted the job, (3) the CO said someone had to go.
And I've seen it enough times where a bro gets ambitious and wants to be secretary or conductor or something. Maybe he'll be gung-ho the first few months, but usually by the second CO visit afterward, his passion is deflated.