Bane can only spread to 3~4 targets from what I've seen (on both SCH and SMN), so you'd have to use multiple banes to dot the amount of mobs you'd be killing in WP speedruns. This is easily tested if you want to try it out yourself - just gather up 4+ mobs in the open world with Bio and then Bane them when they're clumped and you'll notice how there will always be a few that aren't dotted.

I have no idea if this is intended (bad tooltip info) or bane is just bugged.