why do folks want to believe fly fishing is so ridiculously complicated?

MOST of us are not fly-only anglers... most people come to fly fishing after already fishing with spinning or other tackle.... DWM seems to be one of those- SO,

a fly rod able to cast ONLY one "weight" of line would be analogous to a spinning rod with which you could ONLY cast a 1/4 ounce lure with.... just as an example. Of course there is no spinning rod which would ONLY cast one specific weight of lure. It might cast say, a 3/16 to 3/8 ounce lure BEST, but yes it will absolutely be useable with 1/8 to 1/2 ounce lures too...