Mass Effect 3 - 13: Bet you could really go for a bottle of cool, refreshing Tupari!

[Math_Mage]

The "outcome" you speak of is ongoing; it is not fait accompli. Even if you achieve peace, Tali is not certain it will continue; the most they can say is it will last long enough to fight the reaper war.

This is an area where narrative matters. If you don't want your players to reject the idea that organic-synthetic destruction is inevitable, don't spend a significant fraction of the entire series letting them prevent just that by setting the Quarians and Geth on the road to symbiosis, and definitely don't leave an uncertain future. The fact that the future isn't set in stone is exactly what is wrong with the Reaper assertion.

Hostile or not, what we can be sure of is that organics will try to exploit synthetics - if not the existing ones, then they will create new ones. AI has too many advantages not to do so. And even if the Quarians achieve cooperation with the Geth, that will still leave every other race to want AI of their own, particularly since the humans are also palling around with one in their military.

Now obviously Synthesis throws this out the window, which would be why the Catalyst favors this outcome above all others.

Synthesis is just the magic version of one possible outcome of AI (singularity). And if you want to support the inevitable destruction of organics by synthetics, EDI isn't a good direction for you, because her narrative arc is no more aimed in that direction than the Geth's.