As said above, the phrase itself (I and the Father are one) does not inherently mean an ontological equality.
Well, that's the age old question, isn't it?
You need later Church tradition to force that onto the text.

Well you're insisting it should be read a certain way, when every honest scholar will allow it need not be read so prescriptively.
Let the text speak for itself
I wish you would!
There is really no point in discussion since you have revealed your bread and butter.
Sour grapes?
My question is, Can ἐγὼ καὶ ὁ πατὴρ ἕν ἐσμεν be read to infer ontological equality without offence to the Greek?
And the answer is 'yes'.
Does it necessarily mean that?
And the answer is 'no'.
+++
I think the
Biblical Hermeneutics commentary states the case sufficiently:
"Virtually all modern commentators on John 10:30 take the position that the oneness immediately in view here is a
functional oneness, or oneness of will, purpose, and action.
D.A. Carson, The Gospel according to John:
Verses 28–29 affirm that both the Father and the Son are engaged in the perfect preservation of Jesus’ sheep. Small wonder, then, that Jesus can say, I and the Father are one. The word for ‘one’ is the neuter hen, not the masculine heis: Jesus and his Father are not one person, as the masculine would suggest, for then the distinction between Jesus and God already introduced in 1:1b would be obliterated, and John could not refer to Jesus praying to his Father, being commissioned by and obedient to his Father, and so on. Rather, Jesus and his Father are perfectly one in action, in what they do: what Jesus does, the Father does, and vice versa (cf. notes on 5:19ff.). (ref 1)
Gerald Borchert, The New American Commentary: John 1–11:
The statement in 10:30 that “I and the Father are one” has been an important battleground of theology. The first matter to note is that the word “one” here is neuter (hen) and not masculine (heis), so the text is not arguing for a oneness of personalities or personae (to use the Latin concept) but rather something akin to a oneness of purpose and will. (ref 2)
None other than John Calvin made this same argument centuries ago in his
Commentary on the Gospel according to John:
The ancients made a wrong use of this passage to prove that Christ is (ὁμοούσιος) of the same essence with the Father. For Christ does not argue about the unity of substance, but about the agreement which he has with the Father, so that whatever is done by Christ will be confirmed by the power of his Father. (ref 3)
Metaphysical oneness?
D.A. Carson is one of the few who argues, on the basis of many narrow and wide contextual clues, that a metaphysical oneness of essence or substance is also at least partially or tangentially in view. Others who take this position generally cite Carson when they do.
In short, although the words I and the Father are one do not affirm complete identity, in the context of this book they certainly suggest more than that Jesus’ will was one with the will of his Father, at least in the weak sense that a human being may at times regulate his own will and deed by the will of God. If instead Jesus’ will is exhaustively one with his Father’s will, some kind of metaphysical unity is presupposed, even if not articulated. Though the focus is on the common commitment of Father and Son to display protective power toward what they commonly own (17:10), John’s development of Christology to this point demands that some more essential unity be presupposed, quite in line with the first verse of the Gospel. Even from a structural point of view, this verse constitutes a ‘shattering statement’ (Lindars, BFG, p. 52), the climax to this part of the chapter, every bit as much as ‘before Abraham was born, I am!’ forms the climax to ch. 8. The Jews had asked for a plain statement that would clarify whether or not he was the Messiah. He gave them far more, and the response was the same as in 5:18; 8:59.(ref 4)
(This last comment of Carson’s echoes the line of reasoning in Simply a Christian’s answer to this same question, that the Jews obviously understood Jesus to be making himself metaphysically one with God or they wouldn’t have taken up stones to stone him. I’ll defer to Simply a Christian’s answer for an excellent and convincing treatment of that idea.)
An important thing to note with respect to the Trinity doctrine (and I guess now I’m going beyond hermeneutics into systematics, so I hope you’ll indulge me briefly) is that these different kinds of oneness are not mutually exclusive. It is a false dichotomy to insist it could only be one or the other. Logically, the persons could certainly be functionally one and not metaphysically one, but if they are one in substance then surely they are also one in will, purpose, and action.
So, even if all that’s in view in John 10:30 is functional oneness that wouldn’t rule out or trump metaphysical oneness being found on the basis of other passages. Distinction between the persons is one of the major tenets of trinitarianism, so either way this passage supports the Trinity. Indeed, an argument could be made that the very ambiguity of this passage is evidence for both oneness of essence and distinction of persons—the whole Trinity doctrine in a nutshell. (Underline my emphasis).
Notes
1 Carson, D. A. (1991).
The Gospel according to John (p. 394). Leicester, England; Grand Rapids, MI: Inter-Varsity Press; W.B. Eerdmans.
2 Borchert, G. L. (1996).
The New American Commentary: John 1–11 (Vol. 25A, p. 341). Nashville: Broadman & Holman Publishers.
3 Calvin, J., & Pringle, W. (2010).
Commentary on the Gospel according to John (Vol. 1, p. 417). Bellingham, WA: Logos Bible Software.
4 Carson, D. A. (1991).
The Gospel according to John (p. 395).