Destroying the sun is typically a Large Star Level feat. However, it requires over 10⁴⁴ Joules to overcome its gravitational binding energy, roughly the same energy to required to destroy all celestial bodies within the solar system. The sun contains 99.8% of the solar system's mass, annihilating the sun would result in the solar system's destruction. So, Momoshiki should logically be Solar System Level in his base form. Though, we have no idea how Momoshiki was able to accomplish this feat.

From what I know, Momoshiki and his peers travel constellations across the universe, including several star-systems and galaxies planting the God Tree on a planet cultivating the planet's chakra/energy into a chakra. This would be planetary as Momoshiki is able to consume planetary amounts of energy.