You won't get far in the NFL as a safety if your covering skills are poor.
You also need safeties that can come down hill to support the run. Keep in mind Ravens won a Superbowl facing Luck, Brady, and Manning, with Pollard who was not a great cover safety. He intimidated guys coming across the middle. His hit on Ridley turned the tide, he put Gronk on the shelf on a couple of occassions. Safeties also MUST be physical. A young , physical safety like Brooks should have been retained over excessive depth at LB with Chris Carter or 7 CBs. Two ingredients that the Ravens had with each Superbowl team was a physical blocking FB and a knock out safety.
Our pass defense was not very good the year we won the SB. Pollard did have some impact plays in the postseason, but as the league uses more and more spread, pass happy offenses, I don't think Ozzie wants safeties on the field that can't cover. On a side note, I would say Pollard's hit on Ridley pretty much finished the Pats off, but it didn't turn the tide. We were already dominating the second half of that game.
Ravens were dominating the Patriots 2 years ago with 2 14-point leads and lost the game. Why? Patriots running free in the secondary and no one was making tackles. TJ Ward, Ryan Clark, Bernard Pollard, John Lynch all have rings and none were considered great cover safeties. They simply intimidated receivers coming across the middle and were sure tacklers. Brooks is not in the above mentioned players category, but he was the best tackler in the secondary. Weddle, Levine, and Webb will struggle to bring guys down in the open field. I think the Ravens have a strong roster now, but teams will test our small safeties ability to tackle.