I know its completely academic in the scheme of things, but from a rule point of view.

I've just watched the highlights on Hull FC TV. Should the last Catalan try have stood? I find it a bizarre rule that a player can effectively just keep "wrestling" in that way, even completely changing direction once held to score. Shouldn't it be the rule that once he made the attempt to ground it that in order to change direction momentum had effectively stopped and he was held?

I'm not sure why the ref allowed it to continue so long, because he actually grounded the ball at the very first attempt, and he (the ref) was looking straight at it.
At least that was how it looked from where I was sitting.

Imo, the highlights show that both the ref and the in goal judge don't believe he got it down on the first attempt. They gave the grounding were he wrestled his way back up, changed direction and then grounded the ball the second time. The ref then points to that spot. That's what it looks like to me on the video anyway. Otherwise like you say, he would have called the try immediately.

I agree, it looks like they appeared unsure, but the consensus around where I was last night, was that he actually grounded it before the wrestling began.
I also agree that if the officials didn't think he had at that point, then it looks like the tackle was completed.
I guess we'll never know.

They had earlier in the game very promptly signalled a Catalans player being held up in goal so was strange that this went on for as long as it did, while we can say its academic in this game hopefully when they review they will point out that he had et it go on for too long and infact shuld have called held sooner regardless if he was still tryign to ground it.

It would be easy to criticise the defenders and say they should have wrapt him up but they did and probably on instinct expected the ref to call held and was proabbly why Sneyd had a go at the ref