what seems to be lost here, regarding the Safety position, is in Fisher's scheme, the safeties are interchangeable. There is no FS/SS designation. They BOTH need to be able to give support in run defense, and be able to split the field over the top n pass coverage.
If they have plans on adding a safety, I expect it to be someone who is similar to McDonald in skillset, and compliments him rather than a pure FS type player. There were TWO major issues with the safety play this past season. With BOTH players being FIRST YEAR starters, it was asking an awful lot to expect them to be able to make the on the fly adjustments that having veteran guys back there. For all of his physical shortcomings, by having Craig Dahl on the field, they were able to be confident in making the proper calls.
The other MAJOR issue with the Rams safeties, is the consistently POOR tackling. McDonald got better as the year went on, but be it McLeod, Stewart or Giordano, between them, they were the poorest tackling group in the league.
Everyone points to the coverage issues, but for me, unless and until they get better production from the position in terms of tackling, they will continue to stunt the progress of the defense.
Also, the general lack of experience is the main reason for the "scheme" and soft zone coverage in many of the early games. It is just too much to ask a secondary to grasp many of the complex coverages, for example, combination zone/man schemes, and be able to disguise coverages and still be able to make the proper adjustments. Add to that a ROOKIE OLB who never comes off the field, who is still learning how to COVER in these zone calls, and it had a direct impact on what the staff can do. That they chose a "bend don't break" philosophy was the safest course of action.