PS5 also lacks RDNA2 support for DP4a (int8 / int4 and mixed precision), and also lacks RDNA 2's newer ROPs, so can't support hardware VRS. And that wasn't because Sony didn't want these things - PS5 Pro has them now they are available to Sony - it's because PS5's design predates RDNA2. It's mostly a contemporary of the 5700XT, but with some later changes.
As far as I've seen, the only RDNA2 specific feature that PS5 has is RT support, which wasn't originally there because it's not part of RDNA1. Cerny wisely delayed PS5 to make some changes including adding RT support. In almost every other way it's RDNA1.
IIRC, PS5 has the earliest version number of any RDNA design, earlier even than the 5700XT. It was an intended design there at the beginning, when god made the heaven and the earth and the RDNA. It almost certainly came so much later because the PS5 was delayed. PS5 also has the very first, earliest implementation of RT hardware - lower in version number than any RDNA 2 design (1.0 vs 1.1 in PC / Xbox).
The absolute balls on Sony to claim PS5 is RDNA2. It's paid off for them though. Xbox has more features but MS's "everything everywhere" approach to games means they don't get used, while Sony's studios make excellent use of all the features of the PS5.
Whatever MS do with next gen, they need to make sure they have software that uses the features of the hardware to try and sell the platform. No-one will give a shit if the next Xbox has a powerful NPU if MS either don't use it or use to try and provide you targetted adverts.