I think you just nailed the product description, despite what seems a veiled denigration of RME's product update.
From all that I've read, the ADI-2 Pro S/E was always positioned as a limited change in functionality, combined with a shift to an ESS-based DSP chip. During that change, RME added some "minor" but very useful improvements — e.g., ability to send DSP-based channels 3/4 through the second set of outputs on the rear. And they added RIAA support since that was a capability available with the new ESS chip. It was never positioned as a major revision of the ADI-2 product.
Edit: I should add, I absolutely would have preferred those added "so and so" improvements of the 2/4 SE; they would be well worth the added cost. And I would have bought it; except it wasn't released until a few years after I already bought a Pro FS R black.