Both sides neared exhaustion at Singapore

Could stronger leadership or reinforcements have changed the fall of Singapore?

Possibly. The British water situation was dangerous, but the Japanese were also near the end of their supplies and might have had to withdraw if resistance continued.

A counterfactual about transferring Hong Kong's defenders leads to the immediate logistics of Singapore's fall. British commanders feared losing the reservoir and the city's water supply. The Japanese attackers, however, had reached the end of their own supply line and were running out of food and other necessities. Another week of resistance might have forced a Japanese withdrawal, showing how command decisions interacted with exhaustion on both sides.