Currently, unknown.
If a person uses the logic of Devil Fruit vs Devil Fruit then each Devil Fruit can counter another Devil Fruit or if used correctly then there are a few Devil Fruit that could easily be considered "OP" and could easily defeat the Admirals such as Paramecia's Doku Doku No Mi, Jewelry Bonney's unnamed Paramecia Devil Fruit, Ope Ope No Mi, Basil Hawkins' unnamed Devil Fruit, Mero Mero No Mi, Donquixote Doflamingo's unnamed Devil Fruit and Mato Mato No Mi.
But the Admirals aren't depending only on their Devil Fruit due to each of them having mastered at least one/two/three haki and Rokushiki therefore made it harder for them to be beaten. It's possible that there are other pirates, revolutionist or any human in that world that can defeat or fight equally to the admirals but currently, there aren't any shown person that can defeat the admirals due to; short screen time and abilities remain unknown due to plot.
If a person uses the logic of Devil Fruit vs Devil Fruit then each Devil Fruit can counter another Devil Fruit or if used correctly then there are a few Devil Fruit that could easily be considered "OP" and could easily defeat the Admirals such as Paramecia's Doku Doku No Mi, Jewelry Bonney's unnamed Paramecia Devil Fruit, Ope Ope No Mi, Basil Hawkins' unnamed Devil Fruit, Mero Mero No Mi, Donquixote Doflamingo's unnamed Devil Fruit and Mato Mato No Mi.
But the Admirals aren't depending only on their Devil Fruit due to each of them having mastered at least one/two/three haki and Rokushiki therefore made it harder for them to be beaten. It's possible that there are other pirates, revolutionist or any human in that world that can defeat or fight equally to the admirals but currently, there aren't any shown person that can defeat the admirals due to; short screen time and abilities remain unknown due to plot.
Unproven.
