Shepard could have been Saren 2.0, except he would be searching for ways to stop Reapers, building personal army from krogans, geth and Terminus mercs, trying to warn as many as possible and being hunted by governments trying to hide Reaper threat. But we got Loveboad story and it got highest scores in trilogy. So whatever.
People need to understand that Shepard preparing wouldn't have made any difference.
The Reapers are a plot device. There's always going to be as many of them as need be for the story to work. Just like the orcs at Helm's Deep. If the galaxy has 50 dreadnoughts, there's going to be 1000 Reaper capital ships. The galaxy has 1,000 dreadnoughts? There's going to be 50,000 capital ships.
You get the idea. The Reapers are going to invade and crush through the galaxy, at least initially, because that's the kind of story this is and that's what they do. Arguing about numbers is pointless, because it's never been about numbers, it's been about narrative.