"Let alone" and "much less" mean "even less likely or less suitable than" in this kind of usage. There are several ways to interpret the requested usage in the question:
- B prevents condition X in addition to conditions Y and Z
- B prevents condition X even better than it prevents conditions Y and Z (adequate or good for all, but even better for X)
- B is much better suited to preventing condition X than it is to preventing conditions Y and Z (good for X but not really good for Y or Z)
- B prevents condition X even better than Y or Z prevent condition X
Your last example would seem to imply that the last bullet doesn't apply.
For the first bullet, you could use a term like "as well as": "B prevents this, as well as that." In this case, the comma clarifies that the last phase means "in addition to" rather than a comparison of efficacy.
For the second bullet, I'm struggling with a way to use that construction, but you could get the point across using something like: "B prevents this even better than it does this and that."
For the third bullet, again I'm struggling with a way to use that construction, but a way to phrase it would be: "B prevents this more-so than it does that." or "B is more effective for preventing this than it is that." There is some ambiguity as to whether the sentence is comparing the efficacy of B in two uses or comparing B to something else, so the amount of clarifying words needed would depend on the clarity of the context provided by the previous text.
But getting back to the question, that construction is somewhat unique. It works with "let alone" or "much less", but I'm not aware that it can be used for a reverse meaning.