The Rams were also 4th in passing yards, 7th in overall yards, and 11th in points. An off year for a McVay offense, but that doesn't fully correlate with a completely ineffective offense or o-line.
PFF is also a shallow analysis because it is predicting the past (although incorrectly), which is always easier than actually inquiring into what happened (e.g. multiple injuries, inexperience), what factors have changed, and whether the same circumstances will likely occur again.
This is typical of national internet sports reporting where a conventional or intentionally provocative take will typically prevail in the absence of real in depth knowledge of a particular team. This used to be the domain of knowledgeable reporters for local newspapers. National reporters such as PFF now do not have either time, resources or motivation to analyze each team to the same extent or to any real depth.
Shallow or not, 31st or not, will the o-line be as bad as last year again? Imo the obvious answer is that it is very unlikely, for the simple reason that the line last year lacked depth and experience, then was repeatedly crippled by injuries-- the single biggest disruptor for any NFL team.
A reasonable prediction is that if the line stays healthy it will perform much better. No one is talking domination, but consistency and coordinated execution could produce a much different result. Especially with Cam Akers in the backfield.