Is this considered masseter muscle asymmetry? Could it be reduced without surgery? (Photo)

It is impossible, unfortunately, to give you a meaningful recommendation based on these limited photos. It would be in your best interest to have in person or telemedicine consultation with a board certified plastic surgeon, with good reputation in facial surgery. Good luck.

You don’t need surgery or Botox. Symmetry in a skeleton is seen in every single individual on this planet. That includes the skull as well as all the bones of the body. I hope this helps and good luck from New York City Plastic Surgery.