neither of those things use IRC. unless you're just referring to channel-based instant messaging.
Yes. That's why I was using the IRC bridge.
functionally, Discord and Slack have commercialized that model, with clear and obvious effects for people that were using IRC. every community i was part of via IRC has migrated to those services, and i haven't encountered a new community on IRC in forever, but have encountered plenty of new Discord communities
Contrast with HTTP and other related web technologies, whose specifications are so complex that only the largest tech firms can even dream of building their own implementations, let alone achieving full standards compliance. Moreover, those standards are also often driven by those same corporate interests who own significant usage share in the browser space.
To the extent that corporate interests will advocate for standards in their own self-interest (recent example: Google WEI), I would say that the protocol has been commercialized.