You cannot use mastodon from kbin or lemmy. I think you might be referencing the fact that from kbin you can create Note posts, which appear on mastodon, pleroma, calckey, etc as a normal (tweet-like) post.
That's not why mastodon users are hyping kbin over lemmy. There are rumors going around that the lemmy developers are bad people and a lot of mastodon users now consider lemmy blacklisted because of that