Of course people have to work on what is most urgent at that time, that's just business. You can't just work on what you love to work on, unless you have practically unlimited funds.

The CEO doesn't work on what is most urgent all the time.

They work at being the best CEO.

Just because someone is available to be repurposed doesn't mean they are the right person for every urgent matter adjacent to them.

A manager wasting the talents of the talented this way, is the problem in this case. They don't know how to balance their team with their needs.

(Dire one off situations are one thing, but systematic tragic waste shouldn't be defended.)

Most projects of any size have a number of people working on them at the same time. At least to me it seems best if you have someone that is really good at something to keep them focused on that task with momentum and split other portions of the team on the urgent task.