Even with that thought, it's likely to be mostly external base processing occurring in the cloud then localized on the iPhone. Also performance constrained on your ISP/Cell rate/latency. A15, A16, A17 Pro based phones all offer 16 bit neural engine.
iPhone 13/Mini = 4GB RAM
iPhone 13 Pro/max = 6GB RAM
iPhone 14/Plus/Pro/Max = all have 6 GB RAM
iPhone 15/Plus = 6GB RAM
iPhone 15 Pro/Max = 8GB RAM
If Apple offers AI that requires only the newest configuration of Ram/larger neural engine then I think they will get scary laughs instead of smiles.