I've had teams without any of those pokemon, and I wasn't swept by Deoxys. He does NOT take things from 100 to 0. So you can get hits in until he dies like you say you can to Garchomp. I don't see how Deoxys is worse than Garchomp like you say. He does have actual counters. He can be wittled down. I don't even see offense teams being screwed a little a bad thing, though either. =/
First, I'd like to see where I said Deoxys-S was worse than Garchomp. Second, I have said in this topic (that you haven't read) that Deoxys-S doesn't have the OHKO power. It doesn't need it. Taking almost all of OU from 50/60/70/80% to 0%, and outspeeding the entire metagame at the same time is something that no other pokemon can compete with, and it is one of the qualities makes Deoxys-S overpowered in my opinion.