Depending on one's perspective, this could be considered to be fortunate or unfortunate. There are numerous frauds who pedal their own interpretations of what kyusho is. They "add" a lot of nonsense to the application of their techniques (TCM, "circles" of this and that, as well as concern over the time of day).
Anyone who requires the (additional) learning of these extra subjects, is only attempting to (further) steal money from their students. When properly taught, there is no need for these additional subjects of trickery. Proper instruction will provide the student with the ability to understand where and why the "points" are located where they are (and it has nothing to do with "meridians", LOL).
Timing plays a (much) greater role than what is generally being taught (in regards to Kyusho applications). If/when the location is not "ready" (to be struck), then the reaction is/will be minimal (if any occurs at all).
Speed, or power "alone" are pointless, if/when depending on those factors alone. Accuracy is a far more relevant factor if/when determining efficiency. The targets that we train student's to strike, are far more difficult to "hit" than repeatedly pummeling upon an aggressor's head. That doesn't make them impossible to hit, only more difficult.
When (correctly) trained in how to accomplish this feat, it is no more (or less) difficult than any other "skilled" task is to perform. Those that would decry otherwise, are (frankly) too lazy in their own training to accomplish it (or don't posses sufficient ability to do so to begin with).
It should be obvious that all of those factors are necessary/required to make a technique function. Accuracy is just one aspect that will accomplish more (without the other factors), than those other factors will accomplish without accuracy.
Accuracy is accomplished through repeated practice. That practice needs to begin slowly. Over time, the speed of that practice can be increased (the majority of practitioners attempt to accelerate their practice too quickly though, and end up failing in their endevour).
Priority's can be different for each student, but as a starting point, Accuracy should be one's 1st priority, Speed should be 2nd with Consistency and Frequency intermixed, with Power being included at every level as well, but not as being the main priority at any of those stages/levels.