It's not Penang that I think is important but holding NW Malaya. Penang cannot be held without holding the mainland opposite given the forces available (I believe the prewar plan was to leave a battalion in Penang if forced to withdraw South, it's hard to see that making any difference). The British needed to hold Jitra or Gurun to shield Penang, and if they do that then outflanking moves by sea become more difficult, while both the invasion of Sumatra and interdiction of allied supply convoys become much more difficult and less likely, meaning resupply of Malaya is possible.
I think Percival was a decentish staff officer but not suited to command. He dispersed his troops around the peninsular to try to defend everything rather than decide what the crucial area was and focus on that. There were a range of other reasons for the dispersion including underestimating Japan, deterrence (totally undermined when the Germans captured a British defence appreciation revealing how bad things were), prestige, a defence plan based on delaying an advance until reinforcements arrived, and an expectation of more time before things came to the crunch (hindsight is great), but he still failed to command rather than chair the defence.
In the absence of prewar reinforcements and given the difficulty of moving troops from coast to coast in the North, the best options would have been either to concentrate troops in Johore for a siege, abandoning Northern Malaya, or to gamble everything on holding Jitra, sacrificing Kuantan and Khota Bahru. In principle the former might have prolonged resistance and the latter potentially retained Singapore. The Japanese and the rest of the Far East would have have known if either of these were adopted, and in the event of a British evacuation of the East coast the Japanese might well have advanced by sea down the East leading to the fall of Singapore while the British held out in the NW until the Japanese turned north, but at least the British could be resupplied and might have held a defensible perimeter for a while.
Basically, I think there are many ways the British could have done better in Malaya but with hindsight it's hard to see them holding the peninsula without additional forces, and these were never going to come in 1941 unless Britain could somehow generate more resources (fewer losses, larger prewar rearmament, more assistance from the US, France not falling). Similarly, the Dutch might have done better but not dramatically so. It's also probably worth pointing out that strategically the British did OK, their fundamental goals were the defence of India, the Middle East and the convoys along the African coast, none of these required Singapore to be held, although this would obviously make things easier. Singapore was of most value for an offensive strategy in the Far East, that Britain was not capable of until 1944/5.