There's a big difference between the two. For a lot of people on Discord, the fact that the communities are not public is a big feature. That they're sharing information with one company is a much less significant issue (though I agree, it would be better to have a platform that required less).

(That said, I think the fear is a little overblown and borne out of a general distrust of the direction discord is going.)

Discord doesn't require a phone number by default. My experience is that it only does if your IP is flagged.