Your type is tied to a deeper pathology, and it's that level where I think a discussion of strength and weakness is more appropriate. There was a thread that I can't find right now that talked about enneagram types and the "child" inside of them that really got at this. The idea being that underneath our expressed type is a core self that relates to our integration point. If we are unaware of, deny, or actively resist the needs of this core self, then they wreak havoc for us. Getting to a place of acceptance about those needs is what transforms the urges of a wounded self into an expression of integration and wholeness. (This core is the real ballgame to me. If you focus too much on type expression in itself, you're missing a key mechanism, and addressing yourself more to symptom than cause.)
This strength/weakness business is definitely a moot concept as it relates to instinctual variants, in my opinion. Instinctual variants are just a setting: they reveal the dominant locus of the concerns of the core self. So, for example, the challenge of an 8 is to accept and integrate their 2ish core that struggles with issues of connection and giving and receiving love. In the case of an so-first, the core will fixate on love given and received by the community in which the 8 lives. How they connect with and are valued by their society. Accordingly, when the core is less integrated, this is where the 8 is most likely to assert themselves, feel the greatest need to be self-reliant, and be most powerful. As the core becomes integrated, their community as the "other" they give themselves over to, is what they will most want to protect and serve.