Despite Musk's over-optimistic timelines (everywhere not just SpaceX), SpaceX is not the limiting factor for Artemis just because several other critical suppliers (SLS) are even further behind schedule and over budget.

Given their sizes and capabilities, the entire Lunar Gateway space station could be deleted and leave only the lunar-variant Starship upper stage it's supposed to dock with in the same orbit for the crew launch vehicle from Earth to dock to directly instead.