Good points on all sides here. It's situation-dependent. Falk and Marks weren't going to be NFL players no matter what they did. Very good college players who just don't have what it would take to make it in the NFL. Gabe just wasn't big or fast enough. We all know the deal with Falk.
Hercules could have benefited from an extra year, I think, with the way they were planning to give him run at positions other than DT, and that -- perhaps along with gaining some size and other continued development -- could have gotten him drafted. The main issue there was his injury, in any case. Hopefully he can carve out a career.
For some of these guys who are fringe or unlikely NFL talents, they don't have a lot to gain with another year of college, necessarily, but that last year *could* be what would get them over the hump, or even if not, it's another chance to play football, maybe put in work toward a master's degree, etc. An example here was Williams. One reasonably could argue that there wasn't much more he could have shown in a senior year, and Borghi was there to eat away at his role and reputation. That said, he wasn't going to get drafted or make it in the NFL coming out after his junior year, either. Falk and Marks were in similar positions. Over time, most of our NFL candidates will likely be in this boat, owing to the talent pool we usually are drawing from.