3 solid players on the Oline is good enough, even with Eichenberg and Jackson. They're both young too so one of them might surprise still. Every Oline in the league has at least one "hole" too.
I get your worry about Armstead, but he's a stud and will battle through the injuries. Injuries are just part of the game (and yes, I realize he has a history).
Assuming everyone is healthy for the majority of games and the playoffs, on paper we could field a possible Top 12 Oline. With the rest of our roster, a Top 12 Oline will do just fine.