At any rate, the original claim of needing a SSD + a major decompression block to handle PS5 games doesn't hold up to reality. At least according to Ratchet and Clank, which is working just fine on any fast HDD even on systems with 16GBs of RAM, the game is not a data intensive exercise of course, but still.
That portal sequence could very well be designed to be streamed in advance while the player is traversing ahead, especially as each portal contains just a very tiny playable area. Environment swap is nothing new, we've had Dishonored 2 and Titanfall 2 do a full swap in real time in several levels, with unique textures and assets and all, and on last gen hardware. Careful data planning and proper streaming by the developer is the key to this, SSD and decompression block may accelerate this even further, but I would argue that the CPU and GPU of the PS5 may not handle a data intensive game anyway. They are barely able to do current gen games with standard assets at sufficient quality, many times falling into the 30fps lock, or the -frankly quite miserable- 720p~1080p/60fps modes. The main benefit of the SSD and decompression block so far seems to be extremely fast loading times, nothing more.