This is a good point: you need to get your methane leakage rate below 3% in order for synthetic methane to improve the climate-change situation rather than making it worse. Probably the easiest way to do that is to convert it into a liquid fuel, like methanol as I suggested upthread, kerosene as I suggested in a different comment, or ethanol.

At the point where you are doing enough direct air capture of CO₂ to supply a substantial fraction of the world fuel demand, you're also doing enough direct air capture to capture a substantial fraction of world CO₂ emissions. At that point you can just pump some of it into natural gas fields instead of converting it to CH₄.