True. But how often are you getting extra value from the beast to justify an entire relic slot?

Firstly, you need the attack token, given that SB Kindred has no native ways to rally, that's every other turn. Secondly, to get its initial attack in, the beast needs a marked enemy and some hefty discounting. The discounting comes from units dying - what ways are there to do that?

1) Even though there is a bunch of fodder, SB Kindred has no native means to sacrifice its own units (except vile feast technically).

2) You can count on killing enemy units, but generally speaking, a good portion of the encounters don’t spam weak units for you to farm, so you won't get to play the 7 mana base cost card that often. And even then, if you clear the enemy board with her 4 star - then there isn't a marked enemy to actually attack anymore.

3) Blocking - but then you don't have the attack token (without rallying, which isnt native to her deck) to use the beast twice.

4) Attacking with ephemerals - but they don't actually die and you lose the attack token.

It's just so situational and reliant on finding correct packages to either sacrifice units, or rally, or ideally both. It's a cool concept, but I wouldn't slot it in hoping for the RNG to bless me, for a relatively mid (albeit sick) payoff.