You know, the whole Intelligence thing could have worked if they'd kept it as a rogue AI who thought it was obeying its creators' wishes, but had severely misinterpreted them instead. That's basically what they've done here in Leviathan, but they made it about the Intelligence seeking an answer to ending the allegedly inevitable conflict between organics and synthetics, which just pushes the abysmal Synthesis ending.
It would have been better, IMO, if the Leviathans had instructed the Intelligence to just do whatever it took to find a means to protect organic life from dying out. Realizing that all organic life has a finite lifespan, it comes up with a way to preserve the galaxy's sentient life in an immortal Reaper shell to protect them from succumbing to entropy and inevitable extinction. The problem with this idea is, of course, that the Intelligence and the Reapers are deciding people's fate for them, and so the choice in the end would be between destroying the Reapers and leaving the galaxy free to choose its own destiny again, or controlling the Reapers and using them for your own purposes (i.e. domination of the galaxy).
But I guess something like that would have been too simple and too cookie-cutter.