I would imagine that increasing the spacing between the cells actually fixed the problem, while the case and vent are just limiting the PR and financial liability.
I'm guessing at some point, they'll make a change to the Lithium cell chemistry for enhanced safety. Changing the chemistry of the battery, and controller software updates is the real fix. The rest is just failure mitigation.
"If one cell explodes or melts, you still essentially have a fire in progress. Protecting the other cells buys you time, but how much time do you have when there is fire on a plane?"
"Obviously its a design issue, probably very complex that Boeing simply doesnt have the time and money to investigate thoroughly."
"So this is a patch. Nothing I have read indicates an engineering approach was taken to prevent the previous result."