I've done a few of these events, and generally (if they're champion) you need a least 4 people to even ensure their shields aren't constantly recharging. Even if you have a lot of people, he just makes a beeline for the exit once you start hurting him. So far the only one I've completed is one where we had multiple titans constantly punching him on and off. which I'm not sure this is the intended way to win.
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Not impossible but the difficulty on them is way too bleeping high. I've done several and they tended to complete around the 2.5 minute mark when the enemy just ran and kept running to its zone-out.