You call that 'small defeat'?
I always remind our dear drunk brits how their grandpa run like sisi when storm by cycling japs troop from the north. The best part is the canons are facing the wrong direction.
In context of world war scale, yea, just a small defeat, but an embarrassing one nonetheless. US and Britain were the only two true world war warriors. They were fighting practically everywhere, unlike Germany, Russia, Japan and China fighting within defined regions. France had enough spread of colonies then to be fighting "everywhere" but it suffered an early defeat at homeground to Germany. That's a big defeat!
The southward pointing cannon defence was an error, yes. Nobody's perfect all the time. The raiding of Pearl Harbor and sinking of HMS Repulse and Prince Of Wales all indicated a Japanese naval attack from the south. Most British Commonwealth troops were amassed in Singapore awaiting that.
Malaya was left practically undefended as nobody then could imagine that the Japs could cross Indo-China, down Thailand all the way through Malaya on land. Credit to the Jap strategists, they succeeded at the unimaginable.
The Indo-Chinese (Vietnamese), Thais and Malays offered no resistance and let them pass. As promised for non-resistance, the Japs harmed none of them. They were after the Chinese and Brits only. Have you ever heard of any wartime story of Vietnamese, Thais and Malays got tortured or murdered under Japanese hands? The speed and element of surprise came with non-resistance of the locals in the lands, not much fighting involved.
The numerical superiority of troops in Singapore became meaningless and even a burden after the fall of Malaya. The Japanese navy wasn't going to attack from the south for a frontal showdown. They just locked up the sea lanes with their then naval superiority gained from the recent setbacks suffered by the British and American navies. It wasn't a bluff.
The common feature in most Singapore wartime stories was lack of food. The Japanese had control over land supplies with Malaya and the shipping lanes. Singapore could either surrender or be starved to death.