Leareth is like that, Mhalir thinks. That might be one of his core defining traits, that he's - not even just willing to try against the collective consensus, it doesn't feel like a matter of 'willing' to him, he just - figures out what he wants and how to get it, working with the constraints he has, and then does that. The metaphor coming to Mhalir is that, in a world of planets orbiting stars, moons orbiting planets, trajectory laid down by the laws of physics and the pull of a gravity well, Leareth is a starship. He can't defy physics but he's not bound to it, either, he moves under his own power and control. It's a rare trait in Yeerks too, and in humans, both on Earth and Velgarth. It's - part of why Leareth wants Mhalir in particular to survive, because Leareth feels it's a lot easier to start with the raw childish poorly-aimed form of the trait (Mhalir isn't at all offended that Leareth feels this way about him, he's got a point) and teach someone wisdom, than to pull people out of their gravity wells.
And, yes, in a world that contains a great deal of inertia but some agents with the ability and inclination to move against it, you can steer. It's slow and frustrating, Mhalir knows that well, having worked with Yeerk politics for decades. But possible.
(Probably at some point Mhalir should try to explain the Yeerk political factions more clearly to Matirin, because that's part of the cost of executing him, too, he has a lot of sway and loyalty and it's going to frighten his people, if the Andalites he surrendered to end up killing him in thanks for his efforts toward peace. Especially if he carries out the plan with Leareth, for the cleaner takeover of the Yeerk high command, the people loyal to him will see that as an act of heroic courage and sacrifice - he can figure out a way to frame things, probably, that will make his death also read that way, but it'll take some finessing and, if they take that route, he could really use Matirin's help.)
...There's a thought he's trying to form and he doesn't quite have it pinned down, yet, but...it's related to weighing the cost of his death, somehow. He's not sure Leareth has quite found this other framing, yet, and - maybe it would change his mind, if they could articulate it to him.
Leareth doesn't want to die. Most people don't want to die, of course, but Leareth doesn't-want it a lot harder than that, most people don't do anything about this fact. It's partly an intrinsic desire, nonexistence is the worst loss either of them can imagine, Leareth would in a heartbeat choose being enslaved and tortured for a thousand years over permanently being gone from the world. But quite a lot of it is instrumental. Leareth - except his name was Ma'ar, then - was born a long time ago in a kingdom filled with pointless horrors; he doesn't recall much but he remembers his baby sister's infanticide, when there weren't enough livestock to feed the clan that year, and he remembers his mother's death in childbirth, and the first time a man from another tribe tried to kill him to take his cattle. And he remembers Urtho, who was building something wonderful - but, Ma'ar eventually realized, not for everyone. Urtho didn't think of the entire world as his responsibility, and from what Ma'ar could see, almost no one did, and and he saw a future filled with pointless waste and suffering as everyone rode in their orbits forever.
Leareth thought that sticking around to build something better was worth the price of his immortality, he thought he could save a thousand times as many people as he killed to wear their skins - but he wouldn't have judged that, if it had only been about his own personal survival. It would have been the hardest choice he had ever made, because Leareth doesn't want to die, but he wouldn't have taken the option for immortality that involved taking other lives, if he truly thought that there were someone else who could carry on the work in his place. It's just that in two millennia of operating in Velgarth, he never saw that. But if he had...
If Leareth's pattern, Leareth's cleverness and caring and trying, are represented in the world, then...that's enough, maybe? For both of them? It's still almost an unthinkable thought, a yawning abyss, but - if Mhalir could make the future of the galaxy a thousandth of a percent better by ceasing to exist, if he actually knew that with enough certainty, then his own values would demand it of him. There's a lot of galaxy and a lot of future, and he can do math.