I have no evidence to support this, but my gut tells me this will be a very difficult event. As someone else pointed out here, if CLS has such a massive kit, I really can't foresee them making the event a walk in the park.
I've got all my toons at XI and X and I'm still feeling a bit concerned. I'm gearing my X toons just enough so that in case I need to make a last min push to XI to beat the event ... at least I'll be ready in case it does become a huge challenge, even with arena mods.