The issues with Discord over other platforms are highlighted in many other places, but I'll skim over them quickly;
1) BLATANT UNPROFESSIONALISM. Discord is NOT a professional company. It is classic buy-out bait, founded by an entrepreneur solely in the hopes it would get noticed and bought out by a big tech brand like Microsoft for billions. This never happened, and Discord is still a money pit to this day. Why do you think shit platforms like Facebook and Discord allow rampant scams and other nonsense to go on? It makes them more money than the standard user does.
2) Absolute and total lack of privacy features. Discord outright REFUSES to remove user data. You cannot request Discord to delete your messages, only delete your account to 'anonymize' them. Discord messages are totally unencrypted and can be harvested using commonly available open-source tools. You can even see 'hidden' channels using some of them.
3) Zero legal recourse in the event of leaks. Granted this isn't just Discord. But I personally know business owners who had their businesses centralized on Discord and got their accounts hacked through no direct fault of their own. Discord doesn't fucking care. It has total and complete access to their accounts, their servers, everything, but refused to do anything to protect them or reverse the damage. This even applies to explicitly partnered servers. Discord. Doesn't. Fucking. Care.
As it stands any usage of Discord for a vtuber group is an insane liability, which has only yet to be exploited because frankly most vtubers are tech illiterate women who barely understand that a computer has more functions than gaming and livestreaming. At any point, any member of Nijisanji, Phase Connect or any other such 'official' Discord could download an open-source program and use it to anonymously download the entire message history of the server and every member in it, with no way to tell who it was, then just leak it to the public.
Don't. Fucking. Use. Discord. For. Your. Business.