I don't know, more than solars not having real solid themes, I see them as having relative themes, and themes dependent of the other exalts. It seems that the more exalt books appear to compare solars to them, the more the solars meaning and themes seems evident.
I don't like the interpretation of solar charms being about "doing things best". More than just the fact that if it was just that lots of charms and charm trees would be thematically unexplainable, "doing things best" seems like the most uncharitable interpretation possible to such an extent that it looks sometimes...