No, sanatam dharam focus on avatar as well as nirkar swaroop and on bhagwan roop as well, this one aspect you are missing and this is main i.e. Bhagwan which supreme truth. If you are worshipping nirankar that does not mean you are worshipping some other person... Person is same but knowledge is incomplete. When we say Allah or God or Bhagwan here we personify him which is absolute. And you are saying quotes in gurbani in which they say ram krishna allah or other names are references for nirankar brahm.. Then sorry bro i dont agree with you because there are many examples in Gurbani where even places and events or works done by them are mentioned then you can't say it is reference for nirankar brahm.
I have some examples of such kind
Panchali (द्रौपदी) ko raj सभा में ram naam sudh ayi
Hari ka naam sada sukhdai
Everyone knows who helped draupdi in rajsabha according to hindu mythology or history whatever but point is he was not nirankar brahm he was personified God which you say is not mentioned in Gurbani
Second example is from shabd
Bindraban man haran Manohar krishna charavat gaon re ja ka thakur tuhi saringdhar mohe kabira naam re
Everyone know who grazed cows in vrindavan
Listen all the lines from this shabd all the activities of personified God are mentioned not of nirankar pramatma who is omnipresent
Snatna dharam accepts the philosophy of nirankar brahm it is not new.. Even it is mentioned in vedas also that god is omnipresent but but but they also mention bhagwan or personified god is absolute truth and such examples from gurbani also accepts that truth then it's upon you whether you accept this reality or not..