Aftermarket ignition ...do you really need one?

MS Max.

Disagree with your blowtorch analogy. And so does every car maker. Because spark energy & spark plug gap size has increased over time since the days of the Model T.
When you light a blowtorch, you are lighting pure, unmixed gas. When you are igniting a mixture in a IC engine, the mix contains: air mixed with petrol [ the catalyst ] ...& residual exh gas. Exh gas does not burn very well...
Many cars have 0.060" or larger plug gaps. These bigger gaps load the ign system more, which can affect reliability. So there is a cost to make the system more reliable. Car makers do not spend this extra money unless there is a good reason for it......& they do not use big plug gaps unless there is a reason for it.
Many hotrodders do not understand that the rough idle they are getting after installing the big cam is the engine misfiring.........Anything that can increase the heat in the spark will help with the roughness & many people experience this improvement when they upgrade the ign system.