Speaking as someone who's used IRC for nearly a decade and who has developed extensively for it, it most definitely has not stayed simple, what with all the nonstandard extensions every network has brought with it. And while I dislike Discord for many reasons, its moderation tools is not one of those reasons; I'd like to see a good, open chat standard come along that adapts features such as invite tokens, rather than depending on accounts or IP addresses or someone manually inviting you into a channel.

To have a functional, modern IRC client, you have to not only implement what there is in the RFCs (which incidentally, no IRC daemon follows anymore, not even the original ircd2) but you also have to pull in IRCv3, SASL, ISUPPORT parsing, CTCP parsing, a TLS library, ... the list goes on. And for a good experience you also want scripting and the ability to abstract away the differences between services implementations (Atheme and Anope, mainly). Not to mention you have no clientside encryption option on IRC short of any number of buggy OTR implementations.

IRC is not great. It might be okay, but by no stretch is it great.