Nothing wrong with oxy, but arc has it beaten hands down in terms of speed.
Ignoring the time it'd take me to drag the welder out from under the bench I could do a repair like that in less than a minute, if the bike came with the crack ground out.
If I had to reach for the grinder first - maybe three minutes. And that's including clamping the bike to the workbench in some manner.
'Course that also leaves cleaning up the seam afterwards to the owner, but what do you expect for a box of donuts? ;-)