Propane is more than good enough for soldering most plumbing - even above 28mm.
Using a Surefire torch with propane is actually too hot. Remember it's called a brazing torch!
I spent most of my life using a standard blow lamp onto a 2 metre hose attached to a BUTANE gas bottle!!! And it was normally more than capable of doing any joint and very fast on 15 & 22mm. After all, if the solder is melting all around joint, the joint is about at its proper soldering heat. It is not a weld you are doing!
I blame bad soldering mainly on lack of training and wrong flux & its lack of use as well as overheating. Adding a dot of flux to the tip of the wire solder as you solder means the joint stays fluxed & clean & solder flows & capillarys well. You can't solder if you didn't have flux, so why expect to over heat a fitting & for a long period without adding flux constantly? Joint simply oxidises including the edge of the fitting & solder won't stick or flow right. Sometimes danger of pipes being slightly out of line due to walls out of shape if pipes are clipped etc & this can mean pipe is open fractionally more to one side of fitting. This can cause the solder to not stay to the side neatly. So try to keep pipes straight. I know my joints will not leak - ever & I just turn the water on without any worry of any leak. My choice of flux (traditional grease based) is a great flowing flux & gentle on pipe & a big advantage IMO.