Curiosity falls under the "stimulation" heading, as does skill acquisition for its own sake (e.g. video games).

To be fair, the SASS list is more a convenient set of categories, than it is an attempt to be a comprehensive and rigorously-proven classification system. However, it's definitely "less wrong" than assuming everything is about status... yet not so unwieldy as the systems that claim 16 or more basic human drives.

The evolution of a desire for competence is an excellent question. Impulses such as curiosity and systemizing could be related to developing competence.

Systemizing could indeed be useful for your survival, and the survival of those around you, via tool-making, weapon-making, hunting/cooking techniques, etc... So systemizing could be a status-related adaptation.

Yet if your systemizing skills create a breakthrough (e.g. you design a useful tool), then your tribe may well accord you status, enhancing your survival and reproduction.

A desire for competence could also be useful for mating, because competence displays "good genes." This is true of skills that don't provide such obvious survival benefits, such as singing and dancing.

A desire for competence, and adaptations that facilitate its development (curiosity, systemizing), could well be useful for any combination of survival, reproduction, and status.