I can't agree that debuts are worthless... but they are *expensive*, and not necessary to start streaming. They also won't be as big of a boost as you expect. You will have high numbers at the event itself, but you'll only a retain a fraction of those.
If you have the money and want to have a debut, go for it! It can be really fun, a way to have a party with chat and tell people about your lore. But if you don't have the money or desire to do one, don't let that stop you from streaming anyway.
Nuclear hot take incoming:
Vtuber debuts are worthless unless you have an already established community