I thought that as Jobs you don't have any of the class skills at your disposal, vice versa.
Not all soloers are against partying at least once or twice, and the content isn't completely useless to them. After all, that's like saying that in the future all content will be Solo-accessible, which it should not be.
A big no to subjob/jobs.
If I wanted to play FFXI I'd go and play it. It's not as though it's gone yet.