Until mirrored life evolves enzymes to eat non-mirrored sugars, mirrored life will be at a large disadvantage.

But with exposure to our environment, replete with non-mirrored sugars, that sets up a large evolutionary pressure in the direction of finding those enzymes, in addition to the mirrored enzymes they will already have for eating mirrored sugars.

With such evolutionary pressure, it seems plausible mirrored life will evolve those enzymes, even though non-mirrored life appears not to have done so, or at least not retained it. Because there has been no equivalent evolutionary pressure for non-mirrored life to eat mirrored sugars.

If mirrored life does evolve those enzymes, due to that asymmetric evolutionary pressure, then instead of being at a disadvantage, it might give them a temporary advantage over non-mirrored life.