The success rate has nothing to do with where a song originated.
SNSD has a ton of songs by western composers. Genie and The Boys had western writers with Yoo Young-jin and SMs in house composing team doing the arrangement and lyrics (Nathalie Makoma used the original Lyrics with SNSDs arrangement) Alex James did Run Devil Run and Hoot (Kesha sang the guide for RDR).
Some others:
US (Mr. Taxi, You-aholic, The Great Escape, The Boys, Mistake, Ooh La-La!, Twinkle, Best Friend, Boyfriend, Baby Steps)
Sweeden (Genie, Bad Girl, Complete, Tinkerbell, Honey, Beginning, Top Secret, Library)
UK (Let it Rain, Time Machine, RDR, Hoot, Lazy Girl)
Australia (Beautiful Stranger, I'm in Love with the Hero, Born to Be a Lady)
- The entire Japanese album consisted of songs from UMG composers (with the exception of Gee which was E-Tribe)
- I remember hearing Into the New World in it's early days was by a western composer with Kenzie handling arrangement and lyrics. It was going to be a M.I.L.K comeback single before they broke up.
Anyways here are some Twinkle messages~