Double standards is referring to TWO standards. One for women, one for men. One for football players, one for everybody else. It splits the standards into two categories.

Subjective standards could be a good thing–comparing a person against his/her own self.

OR

It could refer to having unique standards for everyone.

For example, if you were accepted into Julliard, which has very high admissions standards, would you rather be judged as compared to your peers or to your own progress? It CAN mean you set the bar higher because of individual ability. It all depends.

But it is not a synonym.

I don’t think these necessarily apply, but a synonym site online suggests hypocricy, insincerity, pretense, duplicity, two-facedness

Example. There is a double standard when it comes to immigration laws for the Cuban people and those for the Haitians. Etc.

At best, one could use the word “different,” “separate,” or perhaps “unfair”

A teacher marking an essay has to use his/her judgement as to the overall quality. The first case is an example of “objective”; the second of “subjective.”

Double standard is just a special kind of subjective evaluation and refers to having different expectations of people depending upon who they are rather than what they have done.