When we mention people solo artists like David Bowie, Michael Jackson, Billy Joel, Iggy Pop, Paul Mcartney, George Michael, Bruce Springsteen, John Mayer and John Lennon, we're being serious, cause these guys had a distinguished successful solo career.
But when you mention people like Steven Wilson, James LaBrie and Daniel Gildenlow, we're kinda kidding around, these people are mainly known for their bands and whatever solo tours or albums they did were clearly side projects, they might as well have been singing in the shower, they don't really count as solo artists imo.