If you have more than 4k hp, even a raw destruction won't kill you outright. Definitely not one Cometeor. I'm not saying it isn't powerful or that you can't use it to wipe a team, because you obviously can. I'm saying it's not as easy as one caster dropping one LB and killing an entire team. You're severely oversimplifying it, or playing really bad.

Sure, it is different if you include damage buffs, hp buffs from the nodes and fever/high - but this is where some of the strategy comes in.