The only thing worse than not enough data, is wrong data.
Personas do not distinguish between what data are — and are not — relevant. Whats even worse, the designer is being fed irrelevant data and doesn’t even know it.
For example: As part of your persona, you have a picture of someone who is caucasian. That is a data point. Now, how is someone on your team going to interpret that data point? Will they ignore it? Or will they subconsciously think that they are designing a product for caucasians?
There’s no way to be sure.
This is why personas are awful. They are bad models, and people don’t even know it.