Honestly I don't even know what oneness or modalism is just weird new terms that properly didn't exist 100 years ago. Simple faith is under so much attack it's actually bizarre all these terms and titles that these scholars come up with etc. Jesus is the Lord simple! Also there brother ignore those ignorant devils who would like ruin your faith an make themselves the authority.
Matthew 28:18, And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth.
Rev 22:13, I am Alpha and Omega, the beginning and the end, the first and the last.
From what I understand, and I might be wrong, but modalism is considering that God has 3 modes, like: He is the Father then He switches to the role of the Son and then switches again to being the Holy Ghost. So that the 3 parts of the Godhead are never all present at the same time, a simpler analogy would be like having an actor to have several roles in a theatre play, having him jump from one character's outfit to the next and appearing as that different character. That's what I understand as being modalism and it's clearly a heresy.
What you believe in, is the true biblical Godhead. "For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one." 1 John 5:7
We aknowledge that there is a distinction in the Godhead and yet just like the scriptures confirm it over and over: that God is ONE. Great is the mystery of Godliness, and Dr Ruckman's & brother Bryan's analogy of the body, soul and spirit, is the only explanation that both respects the distinctions and the fact that God is truly ONE.
Trinitarians are stuck at the 3 parts of the Godhead turning each of them into separate beings making them 3 gods (they won't admit it though), and refusing that God can be ONE, because being ONE would mean that Jesus Christ is also the Father, and they can't accept that so they trade the scriptures for strange terms like "divine essence" to defend their false belief which is another heresy.