When we at the old USN were working on beating the level 11 at 300% we were pretty much facing enemies we just couldn’t kill on more fronts that we could cover with three ships. We thought our best solution was to keep rotating between multiple fronts to draw aggro away from the ship that was meant to replace us. If we were facing such a situation, I’d try something similar.
If you’re interested, this (I swear I’ll update it at some point in time) might prove useful.