I don't know if this is the right forum for this question. Let's see what kind of responses you get. If it's all technical rather than outdoor use, I'll move it to Knife Reviews & Testing.
Brittle is a relative term. Relative to other steels, is S30V more likely to deform on hard impact, or to chip? While we might get a good answer from a metallurgist on that, as a practical W&SS answer what we really need to know is ... will my specific knife blade chip in normal use.
THAT depends on heat treat, hardness, blade geometry, edge geometry, and how you use it, more than on the actual steel. You might want to know if the steel is high carbon or stainless or high-tech stainless. Both S30V and 154CM fall into the last category.
Comparing S30V to 154CM is like comparing granny smiths to macintosh apples.

Same thing, different flavor! We just had a fun discussion on the Buck forum about custom shop 110's in those two steels: which would we choose? I went for 154CM for no discernible reason. It just didn't matter to me, since both would outperform my needs for the knife.