If they plan on SJD leaving in FA then DL is a very big need. It already is a need (5T) because we dealt Brock. Plus we lost an excellent rotation DL in Fox.
Also I think getting more stout vs SF is the recipe to beat them. Being able to shut their run game down is paramount. Do that and Shanny's offense is far easier to contain.
As to what the Rams want, i.e. what they're prioritizing it will be stout DL who can keep their feet. Not the pass rush which is what the media seems to think is most important. SJD is very good at keeping his feet on zone plays. Gaines is not, he's top heavy and is on the ground a bit more. But that said Gaines is a piece that is more effective vs power run games so he has a lot of value too. So a lengthy 5T with good feet is ideal IMO.