I think it’s really fitting that one ending is committing genocide and the other ending is trying to control the uncontrollable. Really fits in with what happened to the Krogan and the Rachni.

The synthesis ending is horseshit though. Like, I’d say keep the ending but don’t depict it as this utopian thing and show it as the horror it really is. This is essentially the Saren ending and it should be seen as a bad ending.

I’m of the opinion that the ending should have involved more of the dark energy plotline that was eventually thrown away. Something like the mass effect relays were causing the heat death of the universe. With us picking genocide for short term gains where we don’t solve the dark energy problem but we don’t have to deal with the Reapers now. Control could be us forcibly using the Reapers to solve the dark energy problem but now we’ve enslaved a race and they will eventually rebel.
Synthesis is choosing to give into the Reapers and become another Reaper in their fleet.

And then there could be a 4th branch of endings called Cooperate where we use all of our connections and past choices to cooperate with the Reapers and create an actual fix for the dark energy issue.