Position group strength rises and falls at every program. And some units take years to rebuild -- PSU has gone from probably the worst major-college OL (due to sanctions) to one of the best, and it's taken 10 years to do it.
At the top levels of college football, games hinge on weakness probably more than they hinge on strengths. One thing coaches do very well is exploit an opposing team's weak unit. So the teams that really compete for championships are almost always well rounded -- basically no significant weakness. Ohio State not only had great players all over the field, they had no weak unit. They had nothing you could attack.
Penn State has the potential to be one of those well-rounded teams this fall. They may not have a top 10 D-line but they'll have a good one barring a string of injuries. They may not have a top 10 receivers group but that is a possibility now, and almost certainly it will be a top 20 receivers group.