MIG Welds vs Brazing for simple bike hacks Given that frames are generally brazed, not welded and given that MIG welding will work on simple bike hacks what are the downsides of MIG welding these hacks?

For example, I would like to make a frame mounted front rack (rather than handlebar and/or fork mounted rack).  I know for sure the welds will be uglier than a professionally brazed job, but are there other issues to be aware of?
The reason that brazing is traditionally used on steel bikes is so that the temper of the chromoly tubes won't be wrecked.  (The high temperatures associated with conventional welding would seriously damage the tubing.)

However, Cannondale, in their push to develop good aluminum bikes, invented the technique of rapid welding (since aluminum can't be brazed, and traditional welding worked poorly).  This technique was transferred to the manufacturer of steel bikes, which is why most modern steel bikes are welded (without lugs) rather than lugged and brazed.

The question is, can you do your MIG welding rapidly enough to not destroy the temper of the tubing?