I dont necessarily agree LBs are key to stopping the run....BUT I do agree that stacking legends anywhere is the most effective use of them on defense. Stacking them at DL/LB/DB - doesnt matter - but load one area to increase effectiveness and limit options of the other team is the best use of defensive legends.
It just seems to be a better choice than if you have them spread out. I have teams done each way - stacked DL, stacked LB, stacked DB - all are effective. The thing is you can almost stack two tiers - DL & DB, LB & DB, DL & LB and still have enough legends on offense to be effective. Its clear than one legend on DL isnt ANY better than none - pretty much the same for LB and DB....easy to be negated. A specialized generic staff will work - for instance a run stuffing DL or LB corps.
I have an all generic LB core on one team and they are VERY effective because the all legend DL keeps them free from blocks. The stacked LB corp team does fine because they are effective in run and pass situations and fight thru blocks when they have to....
Just stack 'em...!!!