Not according to the WHO. They absolutely don't say it's 'perfectly safe'. Saying that it's 'safer' to make it up fresh implies that it's not 'perfectly' safe to keep it in the fridge for 24 hours.
Even if you make it up with very hot water, who's to know that it will ALWAYs kill off ALL of the bugs? And on the odd chance that it's not all killed off, you don't want to give it a chance to breed.
If batch making wasn't safe, if there was any sort of risk from serious illness or death from batch making, then surely the WHO would state 'it is not safe to store feeds', rather than give explicit instructions on how to do it, including how to travel with pre prepared feeds.
If we are talking about e-sakazakii, then either you kill it when you make the feed of you don't. If you do, then you don't need to worry about it. If you don't, then it doesn't matter if the milk is drunk straight away or after a few hours in the fridge - if it is present, it is harmful.
Could you link to any statistics about the number of babies who have died or become seriously ill from a bottle of milk that was made with clean water, in a sterilised bottle, heated to 70 degrees, cooled quickly and stored in the fridge for up to 24 hours?