Hackett even says that galactic history books are being rewritten as a result of the "Leviathan Codex".
Everyone knows about them, the shipwreck trap they use to acquire thralls, and their artifacts post Leviathan DLC. They can't do a damn thing without getting an asteroid smashed into their planet. They can sit down in their ocean trench and bloviate about their superiority all they want, unless they grow some fingers, develop underwater metallurgy and the ability to build spaceships, they are stuck down there.
If it were up to me, I'd drop the asteroid on Desponia regardless of any perceived threat (wish the game would've provided such an option). Those things wrote the Bratalyst, then cowered in their ocean and watched while trillions upon trillions of people were killed across thousands of cycles as a result of their work, and their ancestors don't express the slightest remorse or even acknowledge it as a mistake. Someone has to pay for that, and besides, I'm sure the Hanar would like another colony or something in a million years or so when the planet is liveable again.
Personally? I am too intrigued by their abilities to casually dismiss them to extinction.
That genetic structuring, something in their makeup that allows them to command obedience from organic life is intriguing to me. Plus they do end up helping to fight the Reapers in the end regardless, so that to me makes up for their lack of action in prior cycles given they helped the one that humanity was involved in, so their useful to me, at least as potential baselines for possible biological augmentation.
Imagine a human that could invoke Indoctrination or something similar to it, it would be a intriguing result of the Reaper conflict to say the least, why scavenge and scrap together technology from Reaper husks, use their leftovers when you can create.