Faces extreme competition from Landorus-I as a Scarf user, as it keeps momentum with U-turn, has Intimidate, has Superpower/Stone Edge to beat more threats, and a Ground immunity.
I assume you mean Lando-T.
On Offensive Stealth Rock set Slash Jolly nature first since its best set these days is SR, SD, and STAB. Change the move details to emphasize the use of SD > Fire Blast and have Lum Berry / Focus Sash as the item slashes. Lum Berry provides it some leniency against status users but it doesn't change the fact that Focus Sash is still a viable option. Under your set details it should be Spore as the mention, not Sleep Powder. Yache Berry mention should have details added on Mamoswine, HP Ice Thundurus, and Kyurem-B as well. Under Usage tips "However, it doesn't necessarily have to be used as a lead. Garchomp can force switches against Pokemon such as Magnezone and Excadrill, and you can use Stealth Rock on the switch" should explain in a way where being a lead isn't the only option, because honestly this set is generally the lead to begin with so it's counter productive to say it wouldn't be.
The team options right now is really barren. You need to mention more relevant OU sweepers and wall-breakers that appreciate Garchomps support such as M-Metagross, Nasty Plot Thundurus, PuP M-Lopunny, Double Dance M-Bro as the win condition on HO teams, offensive Fairy Types like Azumarill and M-Gardevoir to provide a Dragon immunity, Charizard-Y, a lot of stuff actually. Elaborate on the Bisharp mention by explaining what it does more in depth such as utilizing Defiant for M-Manectric and Lando-T's Intimidate which both of these hinder Garchomps offensive capabilities as one example. Explain a bit more why Magnezone is a good partner other than just offensive and defensive capabilities because there are a lot of Steel type partners such as Scizor and Lucario that provide equal if not better capabilities than Magnezone on a handful of HO Garchomp teams.
Team options should include Klefki as another Thunder Wave user who has the benefits of being immune to Dragon and resists Ice and Fairy attacks directed at Garchomp. Same deal as the Offensive Stealth Rock with barren team options. Mention partners that handle the other side of the defensive spectrum as well such as CM users which include Clefable, Keldeo, Raikou, M-Slowbro, basically specially offensive sweepers and wall-breakers.
The mega chomp sets need a lot of information in regards to how it's being used and what would go with it so finish up that. Other QC members can elaborate on this but I feel certain that you can consolidate both of the M-Chomp sets into just one anyways with some details in OO for optional moves and variations.
Put in all the relevant details for OO along with anything QC mentioned previously and complete the Checks and Counters section.