There have been gains made by anarchist movements. Much of the major retreats the IMF took in the early 2000s were the direct result of the Direct Action Network, for example. Anarchists were majorly involved in Occupy (a radical mass moment that, i.m.o. because of the lack of a vanguard party, petered out). Long-term sustainability and viability is what they lack. They have had lasting gains in capitalist states (the 8 hour day, etc.), they have had revolutions, but after the revolution starts they can't seem to stick it out.

The important thing about being a communist is about not pontificating on the true spirit of this person or that group. You look at material things you aim to do and see who is against you and for you on an issue by issue basis as you build worker power. Spending time wondering what the true nature of an ideology's followers is is idealism.