I'm going to leave it here as I don't really think much else can be said other than the flaylock wasn't OP. The only reason it did well is the inability of most players to think tactically. Thus, the AR users (usually) continued to run up to point blank range on the flaylock - it's niche. They were then outgunned. This is how niche weapons should work. It never outdid the MD except that the fittings requirements were too lenient.

One intangible problem with generalist weapons like the AR at the time is that it doesn't allow players to learn tactics. because the weapon is an "allrounder" there's no need to learn tactics. Thus, when something comes along like the flaylock, which again wasn't OP, the typical AR user did not react by learning to engage at range - where the AR remains the clearly superior weapon, but instead, closed range and was killed. Thus began the forum whining.

The flaylock was too easy to fit. That is all. The rest can be put down to players refusing to learn, and instead crying on the forums.

I suspect you'll disagree, and fine, but Dust needs more weapons like the flaylock - useful niche weapons and far less like the AR - OP generalist weapons.