From a form point of view you're right, we'll learn zilch, but I don't think Sunday will tell us nothing overall.
It tells us that he came out his last race well and is ready to go again (I know some forum members had concerns about his wellbeing, so this puts that to bed).
It tells us Willie is continuing down the 2m route, rather than stepping him up, so Arkle continues to look more likely.
If he beats Top Bandit far more convincingly it will prove he needed the run on debut and there is significant improvement in him.
It tells us more about his jumping - all horses that head the Arkle market have had freebies from the front, so we get to judge him in line with those efforts.
Willie might say something post race that will make the moving pieces of the Mullins puzzle far easier to decipher (highly doubt it, but we live in hope).