It's undue weight if there is too much emphasis on the minority opinion.  I'd say it's pretty obvious the majority scholarly informed opinion is that Menzies is essentially wrong, and quite badly so.  If there's that much difficulty finding other supporters, and if so many academics are objecting to his work, publicly, then perhaps two critical sources is due weight and therefore appropriate.  If hammering away is the norm, then we should represent that hammering.  Neutral doesn't mean credulous, uncritical or friendly - it means fair weight to the state of the art knowledge.   (t) (c) Wikipedia's rules:simple/complex