What is missed is it's not about 'stopping the run' it is about assignment. Yes, you want make the tackles, and far too many people obsess on these statistics because it is the low hanging fruit, like sacks and qb pressure - all nice fantasy football stuff, but the reality on the field is you have an assignment - often the lineman's job (especially interior if they can create a double team situation) is to absorb blockers and even move them so the linebackers can attack the gaps and make the tackles. This is the fundamental problem I see when talking football - people talk about stats while missing it's about assignment fulfilment. If you handle your assignment and win that battle you generally win the play. Every down lineman's assignment on every play is not necessarily to make the tackle or get the sack - it's to put the LB's or edge rushers in position to do so. Last year the 'read and attack" failed - the split second lost in that scheme by the defense gave opposing offenses a huge advantage
This is why I reject PFF - they simply do not account for that because they do not know the assignment. Is it a stunt, a blitz? Statistics do not necessarily show a players true value - if a dlineman is handling his assignments correctly and others are making the tackles due to his assignment fulfillment - he ends up with 'less stats' when in reality he is just as responsible for the tackle, pressure, etc. the statistic has to land on someone for convenience so blowhards like cowherd can pretend to know what they are talking about (they don't), but it's not necessarily representative of the whole truth.
Adding another body is expected - I assume JS will look hard for interior guys getting cut - maybe even via a trade - and just like the first roster turnover in 2011 - they will add as many bodies as possible until they find the right combination.