You are correct that I am not smart enough to follow your logic. By your logic, SC could have the 14th best OL recruiting in the SEC for 4 straight years, but the the quality of your OL in in 5th year would be unaffected because they don't line up against the other teams OL. I'll keep thinking on that one.
Maybe you have some misunderstandings about JUCOs. The difference between them and high school kids is significant. The JUCO kids take about half a season to a full season to adjust to D-1 football while most high schoolers need a full year. Then you get 1 productive year from the JUCO kid, while the high school kid gives you 3-4 good years. These projections are based on a good evaluation. That's why most big time programs do not try to build on JUCOs, rather they use that route to pick up a player here or there when injuries, early departures,etc have put them in a situation where they need relatively quick help. JUCOs will help sooner than high schoolers, but it still takes time. You need help in the first half of your schedule, and there certainly is no guarantee that Lewis or any other recruit will be ready. UNC, UK, UCF are all games you must win if you are going to have a decent year, and you are counting on players winning those games who have never played a down of college football.
Recruiting rankings are very subjective, but they do have some value. If you look at the team's in last years playoff, you will find that they recruited well the previous 3-4 years. OSU, Bama, FSU are always in the top 5 or so classes, so it must mean something.
Also, I said nothing about your OL recruiting except in the hypothetical just as I did in this post.