Yes, the English language really lacks the vast suite of words we need in order to express our degrees of certainty about things. Words such as "know", "believe", "think" and "suspect" don't express these things properly, but we have to make do with what we have.
I don't think that "believe" is a particularly bad word for the relationship of a rational person to a fairly well established fact, though. I believe, for instance, that the Earth has an iron-nickel core. I fully acknowledge the possibility that it might not, and am fully ready to change that belief based on new evidence, but I think it's fairly well established and I am willing to act as if it were true.
I don't think that "believe" is a particularly bad word for the relationship of a rational person to a fairly well established fact, though. I believe, for instance, that the Earth has an iron-nickel core. I fully acknowledge the possibility that it might not, and am fully ready to change that belief based on new evidence, but I think it's fairly well established and I am willing to act as if it were true.