This Is just comical. Your questions on offense boil down to "Some of the players on O had poor results last season". Then, you proceed to say "All of these defensive players, that couldn't even start last year, are likely to be better than the person they're replacing".
You listed 8 defensive players, only two of which (Ford and Sorrell) were starters last year. The rest were all backups. Yes, they played, but they are mostly unproven. That's why there are so many question marks.
The offense returns 9 starters (10 if you want to count Cain). Yes, we lose the best RB in the country, but that's also usually one of the easiest positions for a freshman to play, and we have 4 or 5 excellent choices including the #1 RB recruit in the country. Otherwise, the only question surrounding the offense is basically "Will all of the players from last year be better this year?" Much of that hinges on Ewers, but even that's not some big question mark.
Versus the defense, where we don't have any clue if either Edge can generate pressure consistently or hold the edge against the run. How will a new DT stand up in the middle with starters' snaps? (Murphy has enough track record to not be unproven). Will Collins or Vasek or Tapp or Finkley or Walton contribute meaningfully? Who's going to play next to Ford? Gbenda, Bush, Blackwell, and all the freshman have questions surrounding them.
The starters in the secondary are likely solid, but we're also expecting lots of contributions from young unproven players. Especially if Catalon gets hurt again.