I tend to rank zetas in 3 categories:
A: Essential/Game-Changing - Completely elevates a character or team to a whole new level
B: Nice to Have - Pretty good, but won't make or break the team
C: Luxury Item - Not particularly good and should only be taken if you absolutely love the character
Out of the classic BH squad, the only A-rank is Bossk's lead. The rest are mostly B-rank: decent additions, but they won't single handedly get you to the next arena tier or anything. A couple, namely Bossk's unique and Dengar's, are in the C category.
I would definitely put your zetas elsewhere, though if you really want another zeta on them, Greedo's isn't half bad. Dengar's is completely redundant with a Bossk lead though - he should be stealthed most of the time, so he doesn't need even more healing.
