You say:

So, my suggestion is to use "rationality" consistently and to avoid using "rationalism". Via similarity to "scientist" and "physicist", "rationalist" doesn't seem to have the same problem.

I think this analogy is inaccurate. The suffix -ist has several distinct meanings, and my impression is that the general public will be apt to understand "rationalist" to mean "someone who subscribes to rationalism" (whatever exactly that connotes in the given context), not "a practitioner of/expert in rationality."

I suppose you have the latter meaning in mind when you make the analogy with "physicist," but I don't think that's how the term is likely to be perceived outside of LW. (Just like e.g. "historicist" doesn't mean "historian.")