In addition to the reasons described there (which are valid, and I agree that they are good reasons to avoid Discord), there are others, such as, you might not have a telephone number (or you do, but it cannot receive SMS), and you might not want to require everyone to register with someone else unrelated to your project. (Also, I have seen that apparently Discord will require face scan, so that is another reason to be avoided; if you do not have a camera (or if you do not want to send a face scan to them) then that will not work.) (And, you should also avoid needing Facebook, etc)

However, I think that IRC can be useful. IRC is not the same as Slack and Discord like they mention, but often the other things are not needed, and IRC also is not too complicated to use and does not require a large web app or other stuff like that, which is a significant advantage of IRC. Also, another thing they did not mention, which can be helpful, is NNTP, which can be used both for announcements and for discussion, like email can be. This way, no web apps are needed, and email subscriptions are not needed; however, it can also be bridged with email if needed.