They have Dacquean Cook and now Nate who can knock down a 3 as well as James Harden but yeah, they're not exactly lights out or anything from 3 point range.
Westbrooks strength is his driving and mid range jumper.
Something that hasn't been mentioned is the Nazr Mohammed pickup which i like too as he's another good interior defender, rebounder and shotblocker and can put in a shot every now and then.
I did like Jeff Green but i think OKC did pretty well today (assuming Perkins stays healthy). Overnight OKC has gone from fairly weak inside defensively and rebounding wise to fairly strong in that department without really having to lose all that much.