Vishnu,Narayana,Vasudeva,Janardana and Krishna have been declared supreme many times in Mahabharata.
Which other Gods have also been declared as supreme, the origin of everything or Brahman in the Mahabharata?
Here are two examples.
The Supreme Spirit hath three condition, In the form of Brahma, he is the Creator, and in the form of Vishnu he is the Preserver, and in his form as Rudra, he is the Destroyer of the Universe.
Mahabharata Vana Parva Section CCLXX
Mahadeva is eternal Brahman.
Mahabharata Anusasana Parva Section XVII