Correct. They lost several key players on a defense that was not good when those players were healthy. They had close to the worst D in the league last season, which is why the lost so often.
On offense, they lost their LT for most of the year, Roddy White played injured at first, then he missed a ton of games. White was not healthy until late in the year. They also lost Julio Jones for most of the year, leaving them with just Harry Douglas for most games. Gonzalez was old and double covered on every play.
Despite all of that, their offense was still pretty good because Matty Ice gonna Ice.
This year, with Matthews at LT and their WR unit healthy, look for them to score big numbers again on offense. They already had two key injuries to LT Baker and their defensive captain Weatherspoon this year. Their D will likely be pretty bad again, but with that offense they should win a lot. People talk about the Phins OL, but last season the Giants and Falcons both had worse OLs than the Phins did. Just think about the fact that the Falcons let Clabo walk and what they replaced him with on the right side was even worse. Once they lost Baker at LT they were a mess. Drafting Matthews was huge for them, but it was still a huge loss for Baker to get injured again this year.