Gasoline will burn for much longer so the energy will be released slower, so the peak will be much lower. And we perceive the peak light not the total amount of energy (see 1000 lumen stroboscope going 1 ms on - 999 ms off vs 1 lumen light turned on constantly).

Also gasoline will release more radiation in infrared part of the spectrum.

The lightning finishes in microseconds. The flame front speed of well-mixed gasoline/air mixture is about 16.5 m/s (see https://en.wikipedia.org/wiki/Flame_speed ) so 6 microseconds to cross that 0.1 mm.

Seems comparable, right? But that's the entire length of the lighting bolt in microseconds, not just one patch. Plus, the 0.1mm calculation assumed only gasoline, not a gasoline/air mixture with a 12:1 compression. Any guidance from a real-life comparison would be affected by the diffusion speed of oxygen. If it takes significantly longer to burn the same energy then the intensity (energy/time) will be significantly lower.

In addition, the spectra are different. Have you ever seen a fuel-based camping lantern? They use a mantle to make the light significantly brighter. (See https://www.youtube.com/watch?v=F3rncxf4Or8 for details). This mean the visible light from burning fuel isn't a good guide for the amount of visible light which can be generated from the same amount of energy.