While I agree, I think there would still need to be some loss for improper co-ordination (we have chat for a reason); and duration is a much better mechanism than potency (which gets messy very quickly).

One solution could be that overriding a buff adds half the remaining duration of the existing buff to the new buff, for example:
NIN-A does Trick Attack, 3s later NIN-B does Trick Attack; NIN-B's Trick Attack would apply with a duration of 10s + (7s / 2) = 13.5s

This would make it more punishing to override buffs early than late, so communication / co-ordination is still encouraged, but it's not a complete loss if you mess it up.