Thats what Hardmode is for.
The last boss drops some campaign on normal, theres your loot variation
Apparently I missed somehow that the last two bosses drop a random BH secondary item (i.e. implant, earpiece, etc.), so I went ahead and updated the post accordingly. However, I haven't seen any indication or video showing that campaign pieces drops off of Story-mode TFB. Where are you basing this information from?