Build wise You should have prioritized finishing the locket over the warden mail because it seems like leblanc was the one popping people before they could really get into the fight.
Vi- should have gotten the health enchantment because your team had enough damage, and she should have gotten a health item over resistance in the zzrot
varus- could have gone for a qss instead of static shiv
as far as position, from the kill placement chart it doesn't look like you guys got caught out too often, just lost team fights.
Without seeing the match I am assuming leblanc would pick someone off then their team would engage and clean up, and without any hard cc I'm not sure how much you could have done about that except maybe if udyr was close enough to who she wanted to burst he might have been able to stun her then chain it with your stun and vi's nock up to kill her and then push back on them.
It seems like you guys did some good warding.
All in all, I think it was a few small itemization changes and probably better team fight positioning.