This despite the fact that both Control and Synthesis show galactic society continuing? In Control, it's almost the same as in Destroy (with the geth still being alive), and in Synthesis, it doesn't seem like so much has changed that the world became wholly alien. Also, Destroy killing EDI is canon, and the geth are extremely conspicuous by their absence; why, after all, would they survive if EDI did not?
And, of course, placing your own ending on a pedestal and claiming that it's the only viable ending and that no future could come from any other is rather like my saying that Liara is the only viable LI and that everyone else is a pale shadow of her who shouldn't be acknowledged in future games; it's unnecessary, exclusionary jerkiness.
I can objectively demonstrate the inherent failure of both Synthesis and Control in regards to the indefinite continuation of galactic civilization as we know it. I've gone into great detail in my Deception Theory thread. I don't like any of the endings. Destroy is not loved by me and I would never choose it as "my ending". It is simply the only viable ending given the assumption of a non-reaper enemy. So don't strawman this into a "placing your own ending on a pedestal" argument. That path skirts dangerously close to personal attack as opposed to a critical evaluation of the presented argument.
The issue with Control is that the Reapers pushed for this in The Illusive Man. He was indoctrinated and this is what he, and therefore the Reapers, wanted. If Control was viable the Reapers would have simply policed the galaxy instead of exterminating organic life. They have millions or billions of years experience and untold cognitive power, but a sole human of 30 odd years is going to figure out what they could not? It's absurd. Policing the Galaxy was actually the Reaper's original mandate; To keep the organic thralls alive and in check was the Leviathan's intent. The Reapers could not facilitate this. Hence the Cycles as a solution. The only outcome of Control is the return of the Cycles down the line. There are other details that are too numerous to post here, but everything about the ending points to Shepard being changed in the transformation from organic to synthetic intelligence.
So the series could continue post Control... BUT!!! Control could work assuming Mass Effect 4 heralds the return to the Cycles. BUT!!!... haven't they said this will be an entirely new threat?
Synthesis shows a lot of things. I don't want to get into all the details, but for synthesis to work the fundamental qualities of what makes organics organic, the very reasons the Reapers claim to do what they do, must be curtailed. A purely physiological alteration will not solve that problem. And let's face it, the physical changes are minor at best. Furthermore, the mannerisms of the people depicted demonstrate a psychological change. Their behavior compared to other endings, their smiles and whatnot show a people too docile toward the beings who just ravaged them. Any player character in such a universe could not function at the behest of the player. You would be, in essence, a reaper program. Part of that synthetic hive mind. It would not make sense for you to have choices. I hope you understand what I'm getting at. Furthermore, if everyone makes up this intergalactic Reaper or these interplanetary diffused Reapers how can conflict exist?