That’s for the booster (the big lower part) not for starship (the upper part that continues to space). They were surprised to have a vacuum engine out. In space there’s no atmosphere so you can’t use fins or wings to change direction. And if the engines can’t move around, you only have thrust and gravity and the tiny attitude adjusters to direct your ship.

You're simply wrong. The non-vacuum-optimized engines on the upper stage are still functioning in a vacuum, and their ability to gimbal to offset the loss of one of the vacuum-optimized engines was planned for.