Originally Posted by
Nyarlko
I consider it to be "Amount of time/effort/resources spent/taken to reach lvl99". It doesn't really matter usually if it only takes 1-2 hours of time spent actually turning in imprimaturs to reach 99 if that's being spread out over several days. In that case, by the time you ding 99, a grinder like me would already have been 99 since the first day and working on improving gear/merits/etc for several days already.
I don't know for sure, but I would guess that like most other sources of exp, the amount receivable is capped to prevent leveling more than once per completion. If it is, then even by your criteria it would be slower than simply killing things.