This isn't the decline of agency, it's feminism and anti-racism creating agency for oppressed people. Traditionally, if a woman or ethnic minority is being harassed in their workplace, they are unable to speak out against it for fear of being fired by their bosses. In this sense, capitalist hierarchies (as the author identifies) are used to enforce gender and race hierarchies. Now that it's become unacceptable to be…
Pure namecalling can be differentiated from libel/slander (saying things that are discreditable), abuse of employees (which presupposes and enforces an extant power relation) or ethnic or sexual discrimination (where the offender encourages the public to discredit a whole group of people).
Claiming that all men are potential rapists would be both slanderous and discriminatory. Calling someone a cunt or a dick on the internet is a public display of immaturity, whichever the sex of the calling and/or of the callee. Insinuating that such namecalling is slanderous is ridiculous, and the claim that it's sexual discrimination doesn't ring true to me. Obviously repeated and insistent immature behaviour towards someone would constitute harassment, but we're not talking of that either - we're talking of someone writing a tweet and then deleting it shortly after.
It's also outside of the sphere where working conditions within a company are affected - someone writing and then deleting a tweet is hardly having a lasting influence. Which means that it's not within the obvious interest of an employer to maintain good working conditions.
What role is the employer then fulfilling? It is an agent for the privilege of female outrage, a modern "lese majeste" that, through the construction of women as an oppressed minority (spoiler: they're not a minority and more of those that speak out are annoyed than oppressed), allows an ill-meaning person to terrorize people without fear of reprisal.
You're also using a different definition of agency: the author uses agency as a term for responsible action by the person (her|him)self, whereas you include people acting on your behalf. The idea of female hypoagency is exactly that women have less of the former and more of the latter than men do, and a widespread criticism of (a particular variety of) feminism is that it reinforces female hypoagency while outwardly claiming a goal of achieving equality. To which the proponents of that particular variety of feminism reply that females need to be more equal than the others, because they are an underprivileged group.