When we say, for example, "James is taller than Eric", we are comparing the same quality in two people. But are we allowed to use this structure to compare two qualities of the same thing? For example, suppose we have the sentences
"This belief is speculative to some degree."
"This belief is factual to some degree."
Now, can we form a comparison like
"This belief is more speculative than factual."
Apparently, the previous sentence can be produced from the following sentence by ellipsis:
"This belief is more speculative than it is factual"
I think a valid way of saying it is
"This belief is not so much factual as speculative."