Henderson's record in the Ballymore is shabby, with only Simonsig really landing a blow for the yard - and he had already run a couple of times over 2m4f in his prep races. Whilst I've little doubt that CH would get further (not sure about Jonbon, tbh), do you really want to test the theory for the first time in a Ballymore? I dunno.
By running both of his, Nicky can completely duck telling one of the owners his horse is inferior to the other. He can legitimately say "I don't know - let's find out in the Supreme", and leave it at that.
I should add, I don't have a dog in this particular fight. I do have an ante-post Yankee with Jonbon at 33/1 included, but two others are dead in a ditch, and the final leg is Energumene in the Ryanair, which seems highly unlikely to be live come the Festival. Even so, I'd just like to see these two high-class novices take each other on, simply for the spectacle I expect them to provide. Throw Sir Gerhard into the mix (thought he was very impressive over Xmas, though perhaps less so than Henderson's pair), and it has the makings of an excellent renewal if all three get to post.