The White Horse Division, of course, was comprised of SOUTH Koreans. Considering you're extolling the fighting qualities of the SOUTH Koreans, who have a fair amount of technological superiority over the North Koreans, and that superiority is increasing every day, that argues that one would NOT need vast hordes of US troops to assist them.
From what I've seen from Korean War vets, other than that horrible initial period before Inchon when poorly-trained and unprepared US units were fed in piecemeal and horribly outnumbered versus North Korean forces, they were pretty unimpressed with the North Koreans compared with the Chinese Communists.
Also, when looking at the fighting record of fairly small forces (like the Turks in Korea, and the ROKs in Vietnam, etc.) Keep in mind that these countries, since they were sending such a small portion of their armies, were sending fairly elite forces; the peformance of these units, while a decent indication of the abilities of their respective armies, might be a bit misleading because the troops they sent were likely far better troops than the "average" forces in their armies.