I've used propane (a bit lower in temp than MAPP) to braze up a few racks for myself using 45% silver. Getting the silver to melt isn't the problem, what is the problem is how long it takes to get even small tubes up to temp to be brazed and the amount of tubing that ends up getting heated as a result.

While I haven't tried it, I fully expect that trying to fillet braze a seatstay cluster with propane (and probably MAPP) would cause the adjacent brazed joints at the top and seat tubes to melt.

I believe that there are videos on youtube showing lugged frame construction with propane or MAPP but the bottom bracket seems to be a problem and people end up building little hearths to help reflect heat back into the joint to be able to braze it properly.