“Disrupts sociotechnological balance. All scientific advancement due to intelligence overcoming... compensating for limitations. Can't carry a load, so invent wheel. Can't catch food, so invent spear. Limitations. No limitations, no advancement. No advancement, culture stagnates. Works other way, too. Advancement before culture is ready – disasterous. Saw it with krogan, uplifted by salarians. Disasterous. Our fault.”
Regardless of who built the relays, Protheans or Reapers, the races of the current cycle didn't, they just found them there lying around, like a child who finds a pill bottle and mistakes it for candy. Put everything in context: the Reaper trap, what it was intended for, and now that the relays are gone, does the galaxy have a fighting chance to survive? And if it does... will they build themselves anew, learn how to compensate for the limitations imposed by the lack of relay network, and get themselves home?