The commercial case is variance testing. A paid social test needs the same person delivering six openings and four asks, then needs them again next month when the offer changes. Booking a creator for that is expensive and slow; a trained identity makes variant forty cost what variant ten did.
The register is the hard part, not the face. Real creator content is badly lit, slightly wrong and shot in a room somebody lives in. Synthetic UGC that arrives beautifully lit reads as an advert and performs like one.
Does synthetic UGC perform as well as real creator content?
When the register is right and the disclosure is handled, it competes on the same terms. When it is too polished, it stops being UGC and becomes a commercial with a phone frame around it.
Do I have to disclose synthetic creators?
Yes. Label to platform policy and to client legal, and put the label where the viewer will see it.