While focusing on Quality and strength of welded joints produced but both methods..
Both processes require the base material temperature to reach welding temperature. Arc welding does this using an electric arc, and the process is quite fast. Also, the deposition of the filler material is fast. This is important because the heat affected zone is smaller.
The heat affected zone is the region when a phase change in the parent material takes place due to the energy being introduced to the material. For steel the crystalline structure changes from face centered cubic to body centered cubic as the molten metal freezes. Therefore, the material shrinks and induces stress in the parts being welded.
Gas welding is a slower process, and the torch flame is on the work piece longer to reach the material’s welding temperature. The parent material conduct more heat away from the torch, and the heat affected zone is larger. There is more distortion to the base metals with gas welding.
Both processes have the pros and cons. Typically, gas welding is reserved for thin, low stress parts. Arc welding is good for structural welding, and higher stress location. Thin materials can be arc welded, but with increased difficulty.
I hope this helps.
It depends a bit on which arc process you compare it to. Broadly speaking there is no fundamental reason why one should be any better or worse than the other.
Perhaps the biggest limitation of gas welding is shielding. A correctly adjusted gas flame will protect the joint from oxidation but is certainly not entirely inert which can be a problem with more active metals (especially aluminium) and alloys which are particularly susceptible to contamination. Certainly for welding stainless steel and aluminium MIG and TIG are almost universally preferred.
Also gas welding is now much less common in commercial and industrial applications so you are more likely to find up to date standards.
Compared to an electric arc (especially TIG) a gas flame is cooler and broader and so the heat affected zone tends to be larger and you end up putting more heat into the work overall. This is more of an issue for some materials than others