I think this isn't quite right, because of the following in the FAQ (https://whc-cdn.games-workshop.com/wp-content/uploads/2018/07/Core-Rules-and-Bases-Sizes-EN.pdf):
Q: If several abilities are triggered at the same time (at the start of a hero phase, for example), how do you determine the order in which they are used?
A: If several abilities can be used at the same time, the player whose turn is taking place uses their abilities first, one after the other, in any order they desire; then the player whose turn is not taking place uses their abilities, one after another, in any order they desire. The same principle applies to any other things – such as command traits or artefacts of power – that can be used simultaneously.
Bolding mine. I think it's pretty clear that even things that happen at the same time actually still happen one after another. And if you have a choice of several abilities that *could* happen at the same time, you don't have to declare all of them before attempting any of them - you can do one, then decide whether or not to do the next.