As I read it, "this" refers to "a monopoly on communication/speech", not "a monopoly [of any kind]".

Messages had to be transmitted by hand until the telegraph era.

The British (or Dutch) India Companies had a stranglehold over shipping -- and thus over communication -- to colonial holdings for much of their existence.

I wasn't aware of this, but I still don't think this is a compelling analogy. I doubt that these companies were able to efficiently parse the content of these messages in order to manipulate the distributions of certain messages, for example. Further, there's simply no way that post had nearly the same share of communication as do digital systems today (most communication was certainly by word of mouth and print).

The majority of communication was still local - and importantly, B/D India Company wasn't opening and reading and censoring all the letters they were transporting.

Benjamin Franklin controlled major fractions of the post offices in the colonies, the other rival post offices and Ben Franklin would often censor mail and remove messages. So, it also applies in the way you originally read it back then as well.

I recommend the biography of Benjamin Franklin by Walter Isaacson

No barrister or legal historian here,

but fairly certain that a monopoly on permissible communication/speech was and is still held (in title at least) by the Crown

this is pretty much precisely what the 1nd amendment is about and why it was so radical at the time.

Also due to the Stamp Act.

The East India Tea Company wasn't a fully antonymous entity though by the time of the American Revolution; it was more equivalent to a state-owned enterprise found in the likes of modern day China. Because of this any "powerful" moves the company made was assumed to be an extension of British political will moreso than that of some profit-seeking NGO.