This verse isn't ambiguous in the slightest. Thomas says "my Lord and my God" to Jesus.
And yet your proposed interpretation of Thomas's statement is about his belief in God, rather than Jesus.
There is nothing in the context of this passage that suggests God the Father is in view.
My understanding of this passage agrees with scholarly consensus. That fact doesn't mean my interpretation must be correct, but it is misleading to call it an "abnormality."
The sheer number of "ambiguous" passages like these that Unitarians have to address for their position to even be possible is enough to prevent widespread acceptance of their views. The contrived "solutions" that they offer for these types of passages provide reassurance to the majority that they are wise to disregard them.
The Greek here is εἶπεν αὐτῷ...With the dative pronoun αὐτῷ like that in the GNT , a statement is directed at someone but it is NOT necessarily being directly addressed to them. So for instance look at the following examples --
ὁ δὲ ἔφη αὐτοῖς Ἐχθρὸς ἄνθρωπος τοῦτο ἐποίησεν. οἱ δὲ δοῦλοι αὐτῷ λέγουσιν Θέλεις οὖν ἀπελθόντες συλλέξωμεν αὐτά;
As can be seen , although the words were said to them ( ἔφη αὐτοῖς ) , they're not even the topic of discussion, let alone being "identified" or "directly addressed."
ὁ δὲ ἀποκριθεὶς εἶπεν τῷ λέγοντι αὐτῷ Τίς ἐστιν ἡ μήτηρ μου, καὶ τίνες εἰσὶν οἱ ἀδελφοί μου;
Again, the one being addressed ( εἶπεν αὐτῷ ) is not even the topic of interest, let alone being "identified" by the addressor. Theodore of Mopsuestia (who attended the lectures of the Greek-speaking teacher of rhetoric Libanius) certainly knew what he was talking about when he proposed this, that the expression at John 20:28 was identifying the Father [in Jesus] even though it was addressed to Jesus.
ἔλεγεν γὰρ αὐτῷ Ἔξελθε τὸ πνεῦμα τὸ ἀκάθαρτον ἐκ τοῦ ἀνθρώπου.
Even though Jesus addresses the possessed man ( ἔλεγεν γὰρ αὐτῷ... ), his words are directed to the [evil] Spirit in the man. Similarly, in John 20:28 even though Thomas addresses Jesus ( εἶπεν αὐτῷ...), his words (either ὁ Θεός μου or else the entire expression Ὁ κύριός μου καὶ ὁ θεός μου) are directed to the Father in Jesus .