In reference to the ellimist and his interaction with the andalites, i think he, at the time, unwittingly mentally advanced them farther than they normally would have naturally. He spoke to them in thought speak back in days that they used hand signs, and when he did they calmed down. Not only that, he used a gun, possibly much like the andalite shredder. now this is a stretch as the andalites took about 65 million years, but it's true that tales of the ellimist were always handed down amongst generations. Did it occur to anyone he unwittingly gave them another possibility for communication?? That in seeing him communicate they had something better to strive for (isn't that how all civilizations advance, at least in human cultures?). Also, taking into account that in TEC he essentially "created" an Andalite Ellimist, using the andalite form, but not necessarily dna?? And the andalite ellimist procreated, we know he lost his child, but none ever said that he had no other children after. even his wife had said they make more babies and maybe they won't die by the virus. Taking this into account, the andalite Ellimist essentially severely contaminated the andalite gene pool, and, while it was extremely slow progress, it was progress nonetheless.
As for who is mor powerful, for every advancement that Ellimist acquired so did Crayak, and vice versa, that's why Ellimist ran and ended up on the Andalite planet to begin with. eventually Ellimist became purely ehtereal, and started undoing things that crayak did in te moments he did them. and eventually crayak found a way to advance himself to ethereal, and here's where we find them. outside of space-time, able to see everything, and able to change everything from that point forward, but it occured to me that maybe they can't change anything that had already happened. If it were possible, then Ellimist would have stopped Crayak at his source