As well as better STABs (Outrage > CC, EQ > Stone Miss), not destroyed by Scizor in a heartbeat, and will secure an easier sweep 20% of the time when your Chomp counter misses and is 2HKO'd.
How has he got better stabs? there even really because CC is better than Outrage but Earthquake is better than Stone Edge. Also you could use the steel berry then Scizor couldn't touch you also Terrakion isn't butt raped by Mamoswine and Weavile. Lastly you just proved my point, Sand Veil is what makes Garchomp Uber plain and simple really.