No planes, no artillery?
Rhee had a squadron of fighter planes, heavy artillery pieces and APCs when the war began. In addition, Rhee had a navy better equipped than Kim's and American advisors (KMAG), too.
The main reason why Rhee's army broke and ran was the rotten officers, typified by Fat Chae, who Capt. James Hausman said got drunk at the news of the fiasco.
How about the no-tanks angle? The KMAG believed tanks were of no use on the mountainous (and rice paddy) terrains of Korea.