Star international first-five-eight Dan Carter polarised opinion last week when it was announced he was taking six months extended leave from the game next year in a bid to prolong his career and reach the 2015 Rugby World Cup.
First-choice All Blacks play aiming first and foremost to peak for the glamour international ties, Prof Grimshaw said.
But that means the fans who go each week to watch them play for their franchises get an under-performing product.
It also means their teammates play with "deliberately self-limiting players''.
It's an issue that is not going to go away, Prof Grimshaw said, especially when there is a dual tier professional rugby system whereby the All Blacks are on a contract system to keep them playing in the country and operating as the brand-focus of the NZRU.
"We need a truly professional system that allows the free exchange of location of players,'' he argued.
"You could argue that the NZRU is merely protecting its product investment by requiring All Blacks to stay and play within New Zealand. The long-term contracts are a way to ensure that players do stay here.
"Yet perhaps we play too many internationals against the same teams. The Tri-Nations was dreadfully stale and, while the addition of Argentina has brightened it considerably, we get an overdose of relentless hyperbolic nationalism that is really just product marketing.
"These are not really teams chosen on who has been playing the best in the competition of Super Rugby, they are instead teams chosen in the main even before the Super 15 rugby season starts.''
If the All Blacks really are ruining New Zealand rugby - a different thing from the brand of New Zealand rugby, Prof Grimshaw says - then it might be time to "rethink what the All Blacks really mean and represent''.
Prof Grimshaw has recently had a paper on rugby, The Oval Opiate, published in the International Journal of Religion and Sport.
In it, he argues that sport and rugby need to be taken seriously in New Zealand as a means of engaging with and understanding our society - as seriously as religion.