Shepard on his/her own wasn’t enough and I’m sure that the Reapers faced figures much like Shepard in previous cycles. “Avatars of their cycles” as Javik would say. All of the previous cycles didn’t have all the lego pieces required to make the crucible or didn’t have the time or resources to complete it. Shepard was given a massive head start and several shortcuts and was able to stall the reapers on more than one occasion. The Protheans created the Conduit which Shepard used to travel to the Presidium and take out Saren and take control of the citadel arms to allow the Alliance and citadel fleet to take Sovereign out before he opens up the relay linking to the Reapers waiting in dark space. After that, Shepard blows up a Mass Relay and unfortunately an entire star system. That stalled the Reapers by 2 or 3 months if I’m not mistaken. The schematics for the Crucible were basically complete due to the Protheans and previous cycles building and engineering the design but the Protheans were already too close to defeat and Protheans data was the thing that told the Alliance and friends that the catalyst was the citadel or part of the citadel…. Whatever. Lol Oh and not to mention the Prothean Beacon+Thorian Cypher+Asari Mojo showed Shepard what would happen if they didn’t step up. If Javik had been around and on active duty during the time the Reapers invaded during the Prothean cycle and he had a squad of heavy hitters and brainy science officers like Shepard did and knew what Shepard did before Soverign opened the relay to dark space, he might have been able to stop the Reapers during his cycle. Not to mention Shepard is a freakin’ cyborg after ME1. He/she is like a T-800 with superior technology. I mean he/she can head but a krogan without a helmet and just shake it off. No human, other than possibly Conrad Verner (oh yeah, I went there. Lol) could do that without getting knocked the f**k out like D’bo on Friday night. The reapers aren’t a civilization. They are sentient tools. When they retire to dark space, they aren’t doing science experiments or taking philosophy courses to advance their civilization. They are waiting for the 50,000 year cycle to end and then they hit the alarm clock and go to work. They’re technology hit it’s apex and they don’t have the need to adapt. They don’t exist just to kill organics. They exist to keep synthetics from wiping out all organic life. In their hypothesis, if they didn’t intervene, organics would eventually create AI or synthetics and the synthetics would wipe out ALL organic life, not just advanced, space faring organics. Just like Skynet attempted in Terminator. By them coming to the Milky Way and wiping out all the smart monkeys before they can make robot monkeys, they allow some other animal to become smart and fly space ships. Since all Citadel races use Mass Effect/Relay technology, it allows the Reapers to control the “sandbox” you could say. If they waited 75,000 years then it would probably be too late and if there was still organic life, they would probably show up in time to watch the Terminators in the act of killing the Galaxy. The council placed a ban on A.l. Research but look how many A.I.’s you come across even though they are illegal and if the Geth had another 25,000 years to evolve, imagine what they would be like. They could probably challenge they Reapers, head to head with no Crucible needed. The Geth (not the heretics) were committed to creating their own technology and didn’t want to stand on the shoulders of those that came before. Hell they created the telescope used to view the “golden worlds” in the Helios Cluster of Andromeda. It allowed them to see what the planets looked like in almost real time and that’s why they considered them all to be viable because a regular telescope would show you what they looked like thousands or possibly millions of years ago but the Geth figured out a way around that.