You don’t step out of the world consensus, you work within it. The reason he wants out is that his mates are conspiracy theorists and want corporations to own health. The motives for leaving are not in the interests of having a healthy world.
There has been a lot of angst re the WHO for a number of years. It was once solely concerned with the effect of disease, it's spread and it's cure.
Sometime before the pandemic , it moved to attempting to sway public opinion on health in an increasingly ideological manner. It became overtly political.
It promoted all sorts of fairly extreme views, including abortion worldwide to full term, teaching children as young as six about masturbation and,chillingly, made recommendations that children between 9-12 should. "make a conscious decision to have sexual experiences or not". We know what that means, and they were not shy of defending the position.
It was craven in it's behaviour towards China during COVID and still is. It has a draft plan to force all member nations to, at it's behest, implement any measures necessary, at any time for what they might think are good reasons.
It's not the organisation it was at all. Nor is it's parent body. There is no consensus. Despite most nations disagreeing with many of their positions, they never yield.
On this, Trump is right, and this time it will have an impact. Last time it didn't, as it takes around twelve months to leave it.
The UK will now be the biggest single paymaster I think. You would wonder at that.