Is it? Think about it like this (not telling your boss what to do) I can braze a joint in half the time using less gas and fewer leaks with 15% than I can with 6%, the chances of having a joint crack upon cool down are increased slightly too. Also, more heat outside the joint = more contamination inside meaning that unless you're using a nitrogen purge, you stand the risk of contamination.
I think if you really look at it, your boss is not saving a dime. Last time I checked, acetylene and labor is getting expensive too...
This in an odd way proves my point, the prep work you speak of does not come free.... I am a firm believer in get it fit, get it brazed and move on. We don't use line sets, so the brazing process for us needs to be as bullet and idiot proof as possible.
X2 on the Stay Brite 8, great stuff IMHO, driers, sight glasses, txv's, reversing valves. I can't see how it would ever have an issue... Even with 410A.
I like stay bright 8 for 410. Don't have to worry so much about draging out the nitrogen. Never had a problem. Still use a lot of 15% silver on commercial refrigeration.