[disoriented]

Any battery with a 70 % imbalance I would treat with extra care.
If the imbalance comes from over-discharge, then a very slow charge might fix it.
(A charger typically will re-balance by shorting a resistance over the higher V cells, allowing the lower cells to catch up. this is a slow process, a balancer like this one might speed this up)

However, if after re-balancing the battery persists in getting badly imbalanced after discharge, I 'd say the battery is ready for retirement. with one cell not holding charge, it won't deliver anywhere near the expected power, and you have the risk of the bad cell going ugly (explode or fire) during charge or discharge cycles.

Agreed. A pack which is repeatedly unbalanced to that extent is not long for this world, and when (potential) crash costs and time are factored in, the cheapest thing to do is to replace the pack.