OK...so let's do some basic Maths shall we George?
Parent A earns £43,000 per year and therefore, under your new rules, will be able to claim Child Benefit
Parent A is married to Parent B, and Parent B earns...yes...you guessed it...£43,000 per year, meaning that, like Parent A, Parent B is entitled to claim Child Benefit.
So let's summarise shall we George? Parent A & Parent B have a combined income of £86,000, and, under these new rules of yours...you know the ones...the ones that are fairer...they are entitled to claim Child benefit.
On to Parents C & D then....
Parent C Earns £44,000, and is therefore unable to claim Child Benefit, Parent D is currently out of work (Let's say a Public Service worker shall we?). This family have a combined income of £44,000, nearly half that of the first family, but they are not able to claim Child benefit.
Apparently, this is a hugely complex problem, and as a result, would need a "Complex system of Means testing" to make it fairer. So what you are saying is, you want the system to be fair, but can neither afford or be bothered, to make it fair.