Clients often ask us why we don't do talent assessment. We do organizational design, and the two seem like they belong together. You redesign the organization, then decide who fills the new roles, so why not have one firm do both?
Because the two jobs work against each other, enough that doing both usually makes each one worse.
To design an organization you have to find out how it really works. You have to get people to tell you where decisions get stuck, which teams duplicate one another, and where power really sits. Most of what's useful is stuff people would rather not say.
People only say those things to someone they trust. That's especially true of the leadership team, and a good diagnostic depends on them admitting where the strategy is vague, where their own areas are weak, and where they disagree with their peers. They'll only do that if they believe the conversation isn't about them.
Now suppose you're one of those leaders, and the firm interviewing you will also decide whether you keep your job. What do you say? Whatever makes you look good. You don't mention that your team could be merged into another one, or that half of what it does isn't necessary. You'd be crazy to.
It also changes what people think about. Org design is about the future. You're working out what the business will need in five years. The best interviews get people to set aside the current boxes for a while and think about the whole company. People who think they're being assessed can't. They start defending the box they're in.
So when one firm does both, the interviews feel more like auditions, and there’s no way to get to the best design for the company.
The other problem is with the designer. The right way to design an organization is to start from what the business needs to do and work backward. The people come later. But if you've been assessing them, you can't forget what you learned. Without noticing, you start drawing boxes around the people you rated highly and designing out the ones you didn't. The structure ends up shaped like your opinion of the current team instead of the strategy.
What makes this dangerous is that from the inside it feels like judgment. A consultant who has spent two weeks with an impressive VP of operations will find reasons why operations should report to the CEO. Maybe it should. But there's no longer any way to tell whether that's the right answer or just the comfortable one.
There's also the obvious conflict of interest: a firm that sells both has a reason to design organizations that need a lot of assessing.
None of this means assessment is unimportant. Putting the right people in the right roles matters as much as the structure. It's just a different job, and it's better done by someone else. If we did both, we'd be worse at the one you hired us for.