Unless Skarm is not sent out and you realize that you're running an EXTREMELY niche move for the chance to hit a threat on an uncommon playstyle. Not to mention that if you mispredict and go for a coverage move/SD for the switchin, and skarm stays in, you could have a very dead landorus. This is a meta where multiple megastones are viable options, you might end up fighting a Skarm that is more than able to take an EQWhat poke would you switch into a Lopunnite Landorus-T? Skarmory? Obvious switch right? Smack down predicting the switch. Then Skarm only has two options. Switch or take the EQ. Landorus-T can now SD or EQ Skarmory or any incoming switch.
I dont run smack down for power.
252+ Atk Landorus-T Earthquake vs. 252 HP / 252+ Def Skarmory: 230-272 (68.8 - 81.4%) -- guaranteed 2HKO
This is against Sablenite Skarm, which is not a KO
252+ Atk Landorus-T Earthquake vs. 252 HP / 252+ Def Filter Skarmory: 172-204 (51.4 - 61%) -- guaranteed 2HKO
This is against Aggronite skarm, which isn't a KO, and will leave skarm with enough HP to Brave Bird you and live.
Not to mention you're running an Adamant nature for this, which greatly decreases your speed in a meta where speed tiers are awkward and having as much speed as possible is best.
252 Atk Landorus-T Earthquake vs. 252 HP / 252+ Def Skarmory: 210-248 (62.8 - 74.2%) -- guaranteed 2HKO
252 Atk Landorus-T Earthquake vs. 252 HP / 252+ Def Filter Skarmory: 157-186 (47 - 55.6%) -- 76.6% chance to 2HKO