Victor Matfield has offered a pointed explanation for Leinster's 41-19 Champions Cup final implosion against Bordeaux-Bègles — the Nienaber defensive system is simply built on a physical foundation that Leinster can't replicate. The argument is that the Bok-style 'outside-in, shut down, no more than two passes' structure depends on tacklers killing the ball at the point of contact, generating the slow ruck ball that lets the defence reset. Without that dominant carry-and-clear physicality, opponents get quick ball and the entire structure unravels — exactly what Bordeaux exposed. Sir John Kirwan takes a different angle: the system demands complete alignment in how players press forward simultaneously, and he argues Leinster's buy-in was fractured at key moments, pointing to Rieko Ioane's positioning on Bordeaux's second try as a symptom of the whole squad not moving as one. Together the two perspectives raise an uncomfortable question for Nienaber's tenure at Leinster — whether the defensive identity that made him a World Cup winner is genuinely transferable to a roster that doesn't carry the same physical DNA.