There is literally one (1) example of any company taking an Embrace, Extend, Extinguish strategy (Microsoft, with the Web, in the late 90s). They went through years of antitrust lawsuits for it.
There are zero (0) examples of it ever working. No, not RSS; no, not XMPP.
There are literally millions of examples of companies, individuals, governments and non-profits adopting open standards and making the network, and their services, better.
More ActivityPub makes a better Internet for everyone.