In the Hebrew, God and Moses are not pushing on the same identical "sea". But the author of this is reading the English and ignoring the Hebrew.
I have no doubt that you're reading genuinely important concepts out of the Hebrew using your own understanding of these things. But the problem that I find not only interesting, but of the utmost importance concerning the proper exegesis of Isaiah 63, is related to a giant, gaping, chasm, in the text as acknowledged in the midrash.
Rabbi Hirsch acknowledges the problem on some level too. Which is why he points out that according to Jewish tradition, Moses' rod is superfluous. In a Jewish understanding, Moses rod is an unnecessary mediator between God's power, and the implementation of that power, since in Jewish tradition it's problematic to envision a mediator between God's power and its implementation. Rabbi Hirsch is fully aware that Moses' rod represents an incarnate avatar of God or his power that lends itself to the Christian concept of an incarnate, singular, mediator between God, his power, and the world.
Rabbi Hirsch knows what so many of the examiners of the midrash know. Viz a viz, normative Jewish tradition has no singular manifestation or visible mediator between God's power, and the created world.
In the scriptural narrative, as noted by the Jewish sages, there's a real, and genuine problem since God clearly anoints Moses' rod as the avatar of his, God's power. In Exodus chapter 4, God goes so far as to make Moses' serpent-rod a portable manifestation of the burning-bush. Moses' rod is the portable burning-bush. And since the burning-bush is the "appearance of God" (as he's seen by Moses), therefore, Moses' rod represents a Mosaic appearance of God and his power.
Ergo, when, in the midrash, the sea refused to part when Moses lifts the burning-bush in his hand, the text has a real and genuine problem. Where do we go from here if the portable burning-bush, the very avatar of the "appearance of God" (at least the appearance given to Moses) fails to cause the sea to obey? Every serious exegete of the text is fully aware that Moses' rod is a portable emblem of the burning-bush. They all know it "represents" the "appearing of God."
So when the text and the narrative see the sea unimpressed with the "avatar" of God's appearance (the portable burning-bush), so that God has too . . . get this . . . appear for real, not in a portable form, not as an avatar, but for real . . . we'll, Houston, we have a serious problem!
Firstly, if God can just appear for real (and every Jewish sages knows that according to Jewish monotheism he can't), then why did he bother with a portable burning-bush? And since we know God empowered Moses with a portable burning-bush, how, or why, does the sea know it doesn't have to obey the portable emblem? What does the sea see, that's a deeper observation of the appearance of God than Moses got to see at the burning-bush?
This question is the question Rabbi Hirsch doesn't want to, isn't prepared to, entertain. This is the problem that makes the great Jewish sages scratch their head to the point of bleeding when the sea gets to see an appearance of God that transcends what Moses saw at the burning bush.
In Isaiah chapter 63, we too get to see something even greater than what the sea saw if we're able to see-saw between what Moses saw, what the sea saw, and what we read in Isaiah chapter 63. Isaiah chapter 63 references the very narrative in our crosshairs, the very midrash we're talking about, because Isaish is willing and able to allow us to see a sight that would make Rabbi Hirsch's eyes sore, Moses' eyes sore, and the eyes of Jewish tradition sorer still: an appearance of God hidden in said narrative and midrash such that Isaiah 63 is the cryptic key pullilng back the veil to see God more clearly than Judaism is traditionally situated to swallow.
John