It’s not an automatic deal breaker, of course. Falcon 9 is obviously a promising success. But Starship is also working with some new challenges that Falcon 9 didn’t have to worry about.
Many of these stem from design compromises that were forced by Starship’s secondary goal of being capable of a trip to Mars. In that respect, it very much resembles another major project to produce a heavy launch vehicle with a reusable combination payload fairing and upper stage that is also capable of carrying a human crew: the Space Shuttle.