The difference is the cadence. Also the rapid pace of development, they aren't afraid to change things and go through multiple blocks, getting data by flight testing and making improvements. Look at Vulcan Centaur and how long it has taken and compare it to Starship.
"ULA began development of the new launch vehicle in 2014, primarily to compete with SpaceX’s Falcon 9 and to comply with a Congressional mandate to phase out the use of the Russian-made RD-180 engine that powered the Atlas V. "
"The Vulcan Centaur conducted its first launch on January 8, 2024, carrying the Peregrine lunar lander as part of NASA's Commercial Lunar Payload Services program. Its second flight, conducted on October 4, 2024, as part of the U.S. Space Force's National Security Space Launch (NSSL) certification process, achieved its planned orbit despite the loss of a nozzle on one of the GEM-63XL solid rocket boosters, which resulted in reduced and asymmetrical thrust. Following a five-month review, the Space Force certified Vulcan for NSSL missions in March 2025. In February 2026, a second issue involving a solid rocket booster occurred, after which launches were paused pending investigation."
Centaur has flown 4 times since 2014. SpaceX began active development of the Starship program in 2018.
"ULA began development of the new launch vehicle in 2014, primarily to compete with SpaceX’s Falcon 9 and to comply with a Congressional mandate to phase out the use of the Russian-made RD-180 engine that powered the Atlas V. "
"The Vulcan Centaur conducted its first launch on January 8, 2024, carrying the Peregrine lunar lander as part of NASA's Commercial Lunar Payload Services program. Its second flight, conducted on October 4, 2024, as part of the U.S. Space Force's National Security Space Launch (NSSL) certification process, achieved its planned orbit despite the loss of a nozzle on one of the GEM-63XL solid rocket boosters, which resulted in reduced and asymmetrical thrust. Following a five-month review, the Space Force certified Vulcan for NSSL missions in March 2025. In February 2026, a second issue involving a solid rocket booster occurred, after which launches were paused pending investigation."
Centaur has flown 4 times since 2014. SpaceX began active development of the Starship program in 2018.