Without getting into a whole “thing” on experts, there is a common fallacy that when your team isn’t performing, you need more of them to get back on track.
On a sorely undermanned project, of course, you might need more senior resources to jump in and get the ball rolling again.
But in most cases, your projects are not at this point and what need isn’t an Expert, what you need is for your existing team to start learning and becoming an Expert.
Better to have people on your team working to become experts than dropping one into the fold for the singular reason that when the team becomes experts together, they grow together, they support each oher and they become stronger than any single expert out there.
Grow the team.