I don't think it's too powerful. It would function similar to Nightmare and Piranas, so they could be built like them with low stats and a focus on strong abilities. Alternatively, they could be built with high stats, but weak abilities to contrast it. If we go the first route, we already know it can function, but it be difficult to find it's niche. The second path would be riskier, but would greatly space CoB from the SoB clans.
The clan wouldn't necessarily be that versatile. Some abilities wouldn't mesh well with certain bonuses.
Why Protect your bonus against Skeelz, Piranas, or Nightmare? Why have ability poison against Freaks? Confidence Vs Frozn, etc. Of course, there would be great combos too, like -8 opp attack, min 3 against Montana.
The CoB would be weaker than SoB against strong bonus clans. You get their powerful bonuses, but you still have to deal with it yourself. A 6P cob may jump to 8P, but the Ulu it's facing goes up too.
The CoB would also be riskier than SoB against weak bonus clans. They gamble their ability to block FPC's extra damage for the chance to deal it. They can DR the cats, but have their own damage reduced too.
And what silly thought is that at the end? No sense to use other clans? The Junkz are the most versatile clan in the game and they're not the most played (they are up there though). As long as the clan is given a weakness (Junkz and their lack of damage), it'll work out fine.

Elpmaxe
2* CoB
5/5
-5 OA, Min 5

A very fair assessment, i guess i was a bit too hasty to judge
nevertheless, i reckon it would really be important to go with the former - low stats with good abilities
thus why i find most of what spikey is proposing is kinda too OP - should go more for Nightmare-like power design (6 average, some 7s with low damage, 1 or 2 8s with even lower damage)

so imho sepulker needs more stars, vulcan should be a 4*, and vorpal is quite OK

on that note, Elpmaxe should be a 3* imho...

Kladenets
4* CoB clan
5/7
-3 opp. power min. 4

Oh, and risthart should be 7/6 imho... 8/6 is just too good a base stats to go with the ability and bonus

Yeah CoB is not that powerful, but it can make miracles on half decks..
and it also force a SoB and SoA matchups.. and if your playing a Mono it's like you're also playing with all clans.

here's my contribution on CoB clan!

Chetchen
3* CoB clan
7/2
Heal 2 max 8

Amphidex
4* CoB clan
7/5
Stop: Power and Damage + 2


Rampage
5* CoB clan
8/4
Revenge: Damage +4
(Frzn beware!)


Fever
2* CoB clan
6/1
Defeat: +3 life

Real nice takkbayak, but perhaps Fever should only be defeat: +2 life since he's 2*
or perhaps a 3* one would also be good 6/4 or something should suit it well

Angst
3* CoB clan
7/3
-2 opp. power, min. 4

Ok screw the CoB clan madness.

Skeelz DESPERATELY needs a new 5* Michael does not cut it. (elo)

8/7 Protection: Power + Damage

if you say overpowered, then look at Heitachi or Dorian. promotes use of Ulu Watu and Bangers, two underpowered clan in elo.

8/7 Prot: P&D is a lot less fair in a clan that has a bunch of other round-winners. That card would just loom over the entire game. If a low-pilled Dr Falkenstein or Sandro or something like that hits you in r1, that card becomes an unfair, super-controlling threat.

8/7 Protection: Power and damage in Skeelz surely wouldn't be overpowered. You gotta remember that in most cases, this card probably doesn't have any use of neither its ability nor its bonus unless you happen to run into DRs or PRs.

Yah @ghelas Skeelz 's main weakness still maintains to be Montana/ Uppers (well mainly Montana) so 8/7 is not that overpowered.

Protection attack clan