Their stats are about equal, except those of Garchomp are all a little higher.
Does this mean Staraptor is just a weaker version of it? Is it worthless to use Staraptor on my team if I use Garchomp?
No, it doesn't mean that Staraptor is worthless. Being that you didn't state your whole team it would all be a matter of type coverage not stat wise. Also an example of where you CAN compare two Pokemon like that would be two obtainable Flying types in Platinum like Noctowl and Staraptor. So check your team based on more coverage than a Pokemon being weaker than the other.