If devs really wanted locked 4k they would do it (by reducing details)
I wonder if this dynamic 4k trend is actually "forced" by Sony to make it easier to scale games for ps5pro/ps6 without the need for patches.
I doubt it's forced, it's just so obviously the correct compromise. 4k is such a high resolution that dropping below that in certain scenes is just so less noticeable than dropping frames.
Until proven otherwise I'm assuming most games labelled "dynamic" will be close to locked native 4k, just with the odd drop to maintain frame rates.
This is based on NX Gamer doing multiple pixel counts of Spider-Man Remastered and finding all the frames to be native 4k, as well as Digital Foundry doing similar analysis on Ratchet and being unable to find anything less than native 4k.
Both of those games (in those modes analysed) have been described as dynamic 4k, so it would seem Sony is being extremely cautious with the native 4k terminology, for whatever reason.