[qb45]

> Couldn't there be a mode, "hey don't fully open these rows, I just one want one random byte as fast as possible!"

As fast as possible is exactly tRP+tRAS. Since the whole row is read in parallel to RAM's internal SRAM buffer, opening only part of it would make no difference.

> What do you mean by "tRP + tRAS"?

Ever heard of RAM timings? I'm afraid at some point you will have to read how DRAM works to understand more. There was a link in my last post.