PowerVR has its roots in a desktop video card with somewhat limited release and impact. It really took off when it was used in the Sega Dreamcast home console and the Sega Naomi arcade board. It was only later that people put them in phones.
In practice, you might think of TMEM like it’s a cache, it’s just that you have to manage this cache manually. You can use as much RAM as you like for textures.
TMEM is also not part of main RAM, like the RSP’s DMEM and IMEM.
NV seems to rasterize vertexes in small batches (i.e. immediately) but buffers the rasterizer output on die in tiles. There can still be significant overlap between vertex generation and rasterization. Those tiles are flushed to the framebuffer, potentially before they are fully rendered, and potentially multiple times per draw call depending on the vertex ordering. They do some primitive reordering to try to avoid flushing as much, but it's not a full deferred architecture.