Some critics insist that Aleksandr Solzhenitsyn, although a great humanitarian, is only a mediocre writer.

a)although a great humanitarian, is only a mediocre writer.
b)despite great humanitarianism, is only mediocre when judged as to writing
c) even when being judged a great humanitarian, is a mediocre writer only
d)even when noted for his great humanitarianism, only a mediocre writer
e)while being a great humanitarian, but only a mediocre writer

This one is fine as it is. All the other choices are syntactically problematic.

The basic sentence here is, “Some critics insist that Aleksandr Solzhenitsyn is only a mediocre writer.” The part between the commas gives you additional information, but it’s what grammarians call a nonessential clause. The sentence still holds up without it.