"I and the Father are one" is more than Jesus saying that He and the Father agree with each other.
The Jews who picked up stones to kill Jesus knew that.
They knew that the "one" was in the neuter and so Jesus was saying "I and the Father are one thing".
Mmmh ... "one thing" is not the way I would translate Jesus' words. The thing is he used the same expression when he referred to the union between himself and his disciples, and between all of them and Jehovah.
John 17:11 “I am no longer in the world, but they are in the world, and I am coming to you. Holy Father, watch over them on account of your own name, which you have given me,
so that they may be one just as we are one. (...)
20 “I make request, not concerning these only, but also concerning those putting faith in me through their word,
21 so that they may all be one, just as you, Father, are in union with me and I am in union with you, that they also may be in union with us, so that the world may believe that you sent me.
22 I have given them the glory that you have given me,
in order that they may be one just as we are one.
23 I in union with them and you in union with me, in order that they may be perfected into one, so that the world may know that you sent me and that you loved them just as you loved me.
24 Father, I want those whom you have given me to be with me where I am, in order that they may look upon my glory that you have given me, because you loved me before the founding of the world.
25 Righteous Father, the world has, indeed, not come to know you, but I know you, and these have come to know that you sent me.
26 I have made your name known to them and will make it known,
so that the love with which you loved me may be in them and I in union with them.”
Was Jesus saying in John 17 that he and his disciples, also with the ones who put faith in Jesus through their word (v.20), are "one thing"? Would you translate "to be one" in John 17 as "to be one thing" as you intend to interpret in John 10:30?
Note that
εις (one) here in John 17 is as neuter as the
one in John 10:30. Understanding what he meant on John 17 with the same wording helps us understand what he meant when he referred to be one with his Father.