JW growth in western countries is almost entirely born ins.
Perpetuating your faith down to your children is why the WT has been able to survive. If parents realised that the teachings today are nothing like the teachings that first persuaded them (or their parents perhaps) then this nonsense would soon come to an end.
I'm a 3rd generation JW and when I step back I realise that if a JW called on my house today there's no way I would accept their easily disprovable nonsense.
So my take on it is that if the cycle of inheriting your parents beliefs could be broken, the decline would be abrupt.
The good news is that western kids today do not blindly accept as much as my generation did, and are more empowered to challenge hand-me-down religion.
The WT may spend billions of hours recruiting but the writing is on the wall. Within our generation we will see the decline begin to set in, and even more so as the WT is held to the light regarding their abusive policies, ever changing unscriptural teachings and blatant money grabbing coersions.