auto body tech here.
the official recommended spot weld cutter size is 5/16.
you have to be exact to completely drill out the weld at this size.
a 3/8 is much easier to completely remove the weld. but as you posted it take more effort to fill those welds back up.

the cheap HF cutters work. but don't last very long before they are dull.
i have use blair rotobroch cutters for years with good results. $$$ but work.