I haven't made baba ganoush this way so take it with a grain of salt, but the way I've approached fruits with similar water content (i.e. squash or apples) is to bake for an amount of time (which is going to give you a more consistent cook all the way through than roasting anyway) and then finish with the butane torch, for a crispy roasted exterior. If you're using a toaster oven without covering, that will already give you some crispiness on the exterior, so you'll likely be able to get the exterior you want with under a minute of active torching.

The sources I can find seem to indicate that butane actually burns at a lower temperature than natural gas, but you make up for this by putting the flame directly on the food, so I'd guess that the food gets hotter (I wouldn't trust sources that say this confidently, as I can't think of a good way to experimentally verify this). It seems like this gives a higher temperature contrast which gives a higher texture contrast between the interior/exterior of the food. It's subjective whether that's a good thing but I personally think it's better.

> and the butane torch isnt gonna put in harmful chemicals more than my gas flame?

I don't know, and I would distrust most sources that claim to know. Natural gas is used for a lot of things besides cooking, so I'm not sure how much effort is put into the purity of the natural gas mixture, and that's putting aside all the piping between source and destination which could introduce all sorts of stuff from molds to plastics. I'm not aware of anyone making claims about the safety of natural gas flames and food. In contrast, butane torch fuels are often explicitly intended for culinary use, and advertising makes lots of claims such as "Near zero impurities" and "No residual oders"[1] (the misspelling is theirs). Without any credible independent verification, I personally don't think these claims are worth anything.

That said, natural gas is a much more complicated mix of stuff than butane, and the chemical reaction of combustion is much more complicated. Butane, in a perfect combustion, should produce CO2 and water, while natural gas, in a perfect combustion, will produce CO2, CO (carbon monoxide), water, NOx and SOx compounds (the latter mostly due to additives to give it an odor). Perfect combustion is a hypothetical reaction that doesn't exist in real life, however, so I can't say how well that hypothetical reaction translates to practical reality.

[1] https://www.amazon.com/Culinary-Universal-Cocktails-Charcute...