In the midst of a song Moses has Israel sing on the eve of their entrance to the land, there's a speech by God about how Israel deserves judgment. In it, God gives an explanation why that judgment isn't as complete as it could have been:
I would have said, “I will cut them to pieces;
I will wipe them from human memory,”
had I not feared provocation by the enemy,
lest their adversaries should misunderstand,
lest they should say, “Our hand is triumphant,
it was not the LORD who did all this.”’ [Deuteronomy 32:26-27, ESV]
If I just had to take this at face value, I would read it as saying that the only reason God doesn't spare them is because that would lead other nations into thinking that they were victors over these people in their own strength. There's nothing here about Israel deserving being spared, because that's the whole point. When judgment is deserved, mercy is not. But if you took this as the only reason God spared them, it's hard to see how God's doing this is supposed to fit into a plan for what would happen perhaps 1500 years or so later.
Now it's easy to see this as not saying exactly that. It's easy to see it as a kind of shorthand for saying that God's reasons didn't have to do with their deserving mercy, giving one example. Other examples related to Israel's enemies abound, including in passages relating to these very events. In the mouth of Moses, we have a larger statement of what Israel's enemies would think of God after freeing his people from Egypt only to abandon them in the wilderness, not keeping his promises to them. So I wouldn't say that this is giving a smaller justification than elsewhere, just giving one instance of the larger reasoning, none of which has anything to do with their deserving it.
Now imagine you're working on a document during the twilight of the Davidic kings, with an aim to capture what you see as true righteous living, seeking to indicate that what's gone on since the time of Solomon has been a rejection of the kind of living the Mosaic law requires. You want to give some hope for those who will still follow God truly, but you want judgment represented in the document as well for those who don't. This is pretty much what the majority view in Deuteronomy scholarship thinks about the book. It's thought by many to have been written as an apology for Josiah's temple reform movement and only pretended to have been discovered in the temple as a long-lost final speech by Moses.
If you were doing this, would you write a song like this, or would you even leave it as is if you adopted an already-existing song? Or would you build a lot more into the explanation for why God spared them, all the while not saying they deserved it? Wouldn't you be insistent on explaining that God had a plan for a continuing Israel, that they would become a great nation, and his promise to make them that nation, while dependent on their continued behavior upon entering the land, nonetheless is a promise that God will bring them to be able to fulfill? I'd expect at least something other than what the nationsare going to think of God, even if that could easily be part of it.
So I'm not sure I'd call this a compelling argument, but it does seem to be at least some evidence, for thinking that Deuteronomy comes from a time when there wasn't this long history of kings who end up with this somewhat messianic figure Josiah leading a reform movement. It actually fits better with the original situation when they didn't know what would happen upon entering the land except that God said they'd be blessed if they follow him and cursed if they don't. At least it strikes me as the kind of thing that would more likely come from someone at such a time than at such a time near Josiah's revival.