The arguments against typically consist of "why shift the worlds greatest centre out of position" and we should use an "actual 5/8".
The world's greatest attacking centre was isolated and wasted in the most crucial game of our season, while Barrett, an "actual 5/8th", enjoyed a glut of possession and did nothing with it. Gasnier's kicking game may be short of the "classical 5/8th" standard, but I'm satisfied that his passing is fine. Either way, I think we've already established that he will not be assuming a "classical 5/8th" role - the abundance of ballplayers (Hornby, Head, Woolford, Young, Caine/Chase/Williams) provides Gasnier with licence to roam. I would've thought that considering he is our best attacking weapon, letting him roam and receive the ball anywhere across the field was a good thing, rather than restricting his vast talents to one small corridor.
Also that the extra defence he may have to endure will tire and perhaps injure him and we'll see him in action less and less.
My response is that I doubt we can see much less of him than we saw in the preliminary final. Tiredness can be managed. Defensively he can be protected if required - what law states he MUST defend as a five-eighth? I think people are being too rigid about each player's roles. Most of them are fluid and interchangeable these days, Gasnier may defend as a centre, winger, even fullback if needs be. Recall when Albert Torrens was named at number 7 in 05. It's just a number on the back and in itself does not define a player's role. Gasnier will be wearing number 6 but he won't be replacing Trent Barrett. It will be an entirely different role for an entirely different player. Gasnier knows how to draw and pass defenders, and his long passing game is fine - witness the final pass for Cooper's try v Storm at Kogarah: running at speed, 10-15 metre bullet to the chest.