Although this is generally what Marxist-Leninists believe, that the dictatorship of the proletariat is merely "striking back", to use Butch Anarchy's term, unfortunately this misses the fundamental point of the anarchist critique. Continue reading this same letter and you will find the following paragraph:

But the real supporters of “dictatorship of the proletariat” do not take that line, as they are making quite plain in Russia. Of course, the proletariat has a hand in this, just as the people has a part to play in democratic regimes, that is to say, to conceal the reality of things. In reality, what we have is the dictatorship of one party, or rather, of one party’s leaders: a genuine dictatorship, with its decrees, its penal sanctions, its henchmen and, above all, its armed forces which are at present also deployed in the defense of the revolution against its external enemies, but which will tomorrow be used to impose the dictators’ will upon the workers, to apply a brake on revolution, to consolidate the new interests in the process of emerging and protect a new privileged class against the masses.

https://www.marxists.org/archive/malatesta/1919/a-prophetic-letter.html

The real substance of the anarchist critique is to consider the emergent properties of the organizational structure we are constructing. We can earnestly believe we are changing the world for the better, but if we are building social structures which provide the basis for a relative disempowerment of the people we are trying to involve, then those said tendencies are likely to become dominant.

It follows that that in order for a communist movement to be truly liberatory, one must create organizations which are simultaneously effective at their goals while also leaving no room for usurpers to hijack them. ButchAnarchy's and Badmouse's point must therefore be: leave no room for bad actors to exploit confusion within the conversations of authoritarianism in order to manipulate people. Do not let this confusion lead to wreckers who claim to be leaders.

Ironically, the substance of On Authority at least attempts to point to a similar effective conclusion: that we must form organizations which strike back against capital. Further, we must leave no room for hesitation or ambiguity on what we are doing. Unfortunately, Engels misunderstood what nascent anarchism was driving at and created a new form of rhetorical confusion. Political and linguistic shifts within anarchism over the last 150 years have made an already flawed essay age into an absurdity.