It indeed is one of the best. Only Rotom and Latias are reliable, and you can't even switch in, because it is a 2HKO. So Landorus will at least kill one, and if these 2 pokes aren't in the opposing team, then you have a sweep.
Ice Shard Mamoswine too, but I didn't say it because it can't tank a hit from Landorus. Rotom-W and Latias if at near full health HP, then they can take a hit and OHKO in return.
I'm actually in favor that Landorus should be banned, but damn, I'll lose so many of my teams.