people mistake flex as the new-LFR-just-without-tool.
as OP obviously seems to do.
now that guy wanted something different. he wanted a serious, quick, problem free run with geared and experienced people. hence the requirements.
thats the nice thing about flex. your raid, your rules. you want an LFR like run? "LFM FLEX you dont need to know anything, we are 5 people carrying the raid!". bet that is what OP looks for. well, that guy's group seems not to be the right one then.