Cassyva’s 1 mana ping requires another minion, spell, or attack to make it effective. Otherwise you’re killing a 1 health minion with a 1 mana 1 damage spell, which is fair. Especially after the Shadow creep changes too.
Starhorn’s BBS is widely considered to be THE worst. I’m not sure what 8/8 creature you’re referring to, since it also gives his opponent a free draw as well, it evens the playing field.
Lillith’s BBS is ironically considered to be one of the most balanced. It’s 1 mana for 2 1/1s with no special effects. While it does have good synergy with other faction cards, the Wraithlings by themselves do nothing outstanding. It’s right on par with Zirix’s BBS in terms of flat value.
Every other BBS plays fairly with the game. The next closest one is amusingly enough Faie’s, which can do upto 10 damage for 1 mana. But that also requires the opposing player to be a complete and utter idiot. Kara’s BBS is the only one that alters the very fundamentals of the game.