What's the deal with Landorus-I?
I'm seeing a noticeable drop in usage for Landorus-I yet I'm hearing it's solid in the meta but like this thing's usage managed to peak 38.01% usage in the São Paulo tornament for reg f, but only made a 7.61% usage in NAIC (Source: Labmaus). Not to mention it's fall from a 19.20% usage in reg f ladder to 8.10% in reg g ladder (BO3 source: Pikalytics because Munchstats doesn't have reg f stats)
It's not like the introduction of the restricteds Caly-I/Kyogres is the sole reason for Landorus-I usage to drop. It pairs well in rain teams for accurate sandsear storms and the ground type is just an overall amazing offensive type against Miradons, Incineroars, Raging Bolts and Torns.
Also, why is there a rise in choice scarf sets? Is it because having a base 101 speed in this format is relatively slow against the 135 ones?
Not much to add on from what Luna said, but here's my input.
- As mentioned above, Landorus

excelled at beating the meta core in Regulation F. It can't really do that now with these teams coming packed with CIR

and CSR

, as well as other powerful restricteds pretty much all being able to OHKO it. It also sometimes just doesn't hit hard enough in this new, more powerful and bulky format.
- Landorus

really can only beat Miraidon

, but only if you have the speed advantage since you get OHKOed via Draco Meteor. Zamazenta-C

is the only other good matchup, yet these teams normally pack Pokemon such as Chien-Pao

and Urshifu-R

which can swiftly KO Landorus

.
- As mentioned before, a speed advantage is necessary to beat Miraidon

. That's where Choice Scarf comes in. Specifically next to Kyogre

, Choice Scarf Landorus

can spam Sandsear Storm. Not to mention, this Pokemon out speeds common Choice Scarf users like the Urshifu

formes and Chi-Yu

. Still a good Pokemon, just you don't have as many reasons to use it.