Missing tackles is the last stat anyone should use for this purpose. Nikorima missed 22 tackles against the cheats, dragqueens and grubs (8, 7, 6). I have no idea why people would want him defending in the ruck.
The best thing you can say about Kodi, is that he at least put his body there, unlike his captain...
Nevertheless, I never understood this obsession some have about a half's defense. It will almost always be the weakest link in a team.
Sure, some are a bit worse than others, which is why having a guy like Gillett around is pretty handy, or a Gavin Cooper for Thurston, or a Tunza for Locky, etc...
It comes with the territory and is supposed to be made up for with attack and organisation.
While Niko does have his moments, he won't ever be a halfback, and his deficiencies don't make up for the benefits in the 7. He's a fullback or a running 5/8 at best.
I honestly don't know who is playing well enough to claim the position, and Dearden is obviously still a kid who probably needs a bit more maturing and toughening up, but I can't imagine anyone in the ISC being much worse for the task at hand.
Said it before and maintain it. You can't dump the captain just like that, but you can move him out of that critical position, so he can hide on the wing (while Isaako reflects on his form in the ISC), then slot Kodi at FB and someone, anyone at HB. In the end you're only dropping one player, while giving the spine a much needed shake up.
Of course, to make
@Morkel happy, it all stands and falls with respecting the footy, completing your sets and attitude to defense.