The problem is that FF isn't lacking in what it does well (providing defensive buffs). So, adding absorb honestly would certainly differentiate it from cold's buffs... but it would not make the set very much better IMO. With all these sets that came out much later than FF, the reality is far too many sets have far too many tools and FF was left behind due to the power creep. Sets like Time, Cold, Nature, etc. all outperform force field. It's because those sets offer both offensive and defensive abilities. And, in some of the sets, heals too. Not every set needs to be that versatile, but if you want to keep FF mostly the same for the "Cottage Rule" but also bring it up to speed... I think adding some sort of debuff that increases offensive ability (like -res) OR adding some sort of offensive buff would make it a much more useful set.