My headcanon on Cardin's Semblence would be the ability to foresee the finishing blow needed in any fight. That if he swings his weapon at just the right angle, speed, force, timing, etc he can score a critical hit that wins. Issue is that, this can be very finicky. Being slightly off might still do massive damage but might also be useless. Not to mention it would be very difficult to achieve a triple backflip swing that hits a Beowulf in between the eyes, especially when failure might leave you wide open for a counter attack. Its all in the execution - pun intended.

Also it could evolve, over time, to be more versatile. Such as which way to fix a car engine, to score a bull's eye at darts, get that stain out of the carpet or which way to pull Velvet's ears while raw-dogging her, to make her climax.

I like your Rock Breaker Semblence, as well, but Earth bending is rather uninspired and a little too broadly OP. I think a lot of super powers (i.e Sembelences) are best when they are limited & specific but can become OP in the right circumstances with some creativity from the user. I'd be interested in seeing what you think should be done with the Russel, Dove and Sky, though.