Obviously in the present context "synthetic" refers to fuel produced using renewable energy. If you are willing to use petroleum, you don't need to synthesize anything because that is where you started, unless maybe you are turning NG into kerosene. But that would be a dead end technology, so would not return investment.

Energetically, the principal synthetic fuels will be anhydrous ammonia and hydrogen. Capturing CO2 to make methane and kerosene is possible but more expensive. In particular, you need hydrogen as input, and must both capture and crack the CO2.

But for some uses you still need hydrocarbons, at least for now. Given carbon taxes subsidizing synthetics, the synthetics could be competitive.

In the longer term, aviation does much better with liquid hydrogen fuel, but it takes new airframes or, at least, extensive retrofits.