the 102 base speed stat is an amazing stat because it outspeeds the crowded (and powerful) base 100 stat consisting of threats like Kangaskhan-M Gardevoir-M Charizards-M etc and even the base 101 of non scarfed Thundurus-T.
Not only that, but Garchomp has spectacular dual stab. Ground/Dragon coverage is great and powerful reliable stab in EQ and then a great move to lock yourself into in Outrage add onto the amazing speed tier. EQ is a base 100 power attack. After STAB, it is not a move to take lightly no matter if a Hippo/Gliscor or an offensive user like Garchomp or Excadrill uses it. SD allows Garchomp to just tear thru teams or make large enough holes they can't recover from and is a common component of Sashed Chomps' movesets. Even without SD, the banded variants let this fast-enough beast tear things up and often time nails typical switch-ins so hard that the victim has to alter their gameplan accordingly often time helplessly sacking off a very important part of their team or switching out into another mon who also takes a serious hurting, ultimately resulting in a losing game. The Scarf variant is able to outspeed key threats like +1 ZardX and a fresh MBlaziken that can only get a Protect up for 1 boost as well as other scarfers like Landorus-t, Hydreigon and Thundurus-T.
Defensively, this thing has access to the ability Rough Skin which just by having allows it to do 1 layer of spikes or SR worth of damage including breaking sashes of contact attackers if not KO em and win in tight games such as a game decided by a Scizor bp KOing chomp only to lose to Rough Skin damage or especially Kanga fainting by going for Sucker Punch or being forced to eq, being KOd before it can move (depending on the game situation of course). Also includes worn down Tflames and Blazikens KOing themselves to Rough Skin and losing even though they KO you based on their hp and the game situation. Rough Skin allows Garchomp to act as a much more valuable sack piece than other Mons due to this ability as nailing a nifty rough skin contact can change a game around at times.
Dragon/Ground is also decent defensively as it gives you notable resistances such as an immunity to Electric type attacks, a Fire resist, and Rock resist.
Not the best defensive typing but due to its stats 108/95/85, especially that HP base stat, it can survive many unboosted hidden power Ice (and still manages to not be guaranteed KO by some slightly boosted). Due to its typing and defensive stats, it manages to survive HJK from Adamant Mega Blaziken even after SR! LO Blaziken, who hits slightly harder than MBlaz, still has a ~50% chance to OHKO Garchomp after SR. Garchomp is bulky enough to survive Banded Brave Bird from Talonflame and +2 adamant TFlame Brave Bird is still a roll vs Garchomp! This general bulk is a big deal which can be easily overlooked
+2 252+ Atk Talonflame Brave Bird vs. 0 HP / 4 Def Garchomp: 169-201 (92.3 - 109.8%) -- 56.3% chance to OHKO
Not only that, you can further enhance Garchomp's defensive use with Rocky Helmet and/or a less invested into attack ev spread with more emphasis on bulk. You can even run Substitute viably with Garchomp due to the base hp, so that even seismic toss can't break em!
this Mon can also function as an offensive SR setter depending on your team's needs.
In conclusion, Garchomp is a Pokemon with phenomenal stat distribution, great offensive typing and decent defensive typing that can do various things very well and has an ideal base speed stat due to the fact that it edges out the highly cluttered (and threat-riddled) base 100 speed tier which makes this Pokemon as commonly used as it is!
