Indeed, if I were the developers I would be threading much more carefully. While it may be true that the letter is not precise enough, access to YouTube implies a relative acceptance of the terms of service of providing the service, and it is not so clear cut as Invidious claims.
Heh writing the application was part of the fun! :D No, really, I think that at least in Beehive, it is an important step: It ensures a minimum understanding of the environment of the instance and its mission, and as long as the option to join other instances is there, why not?