entwine fails against someone whose going to be outdamaging you and can simply blind you to fuck your primary wield - entwining 1v1 works only when you are gonna win regardless, not when you are going to give him 3+ rounds to outmelee the crap out of you. Yeah, there are ways to cover the vulnerability entwine gives you, like balance or maelstrom, but then you'll be at even more of a disadvantage since you had to spend one of your precious legacies just to cover it.
Yeah, there are counter tactics to cover your strat, but then I can counter your counters, etc ad infinitum. No legacies, no uberspecial sets, or cabal abilities involved, an stsf dagger spec will tool any dwarf who attempts to entwine/flurry. After all the rest is factored in, it depends more on situation, but a dwarf entwine flurry spec will always be at a certain disadvantage, since he requires legacies + equipment + preps to cover his weaknesses, while stsf can use those things to gain a bigger edge over him.