'correct' is definitely gradable and is commonly used as such. There is a nice long history of such usage going back at least a quarter of a millennium.
"Which is more correct? This or that?"
There's even "most correct" as in "it is most correct to choose..."
This is due to the simple fact that in many non-trivial fields, correctness is not absolute and thus multiple correct choices or outcomes are valid. Local preferences might recognize this, but prefer one over the other. In noun usage, this is a carryover from verb usage
"My shoes were mostly corrected by the cobbler." is perfectly fine, so users of English also find that "The fit of my shoes is mostly correct." is also perfectly valid usage.
More examples:
Which partial phrase emphasizes, and persuades better a point better (as a matter of rhetoric)?
"It is most correct to take this option."
"It is a preference to take this option."
Of course the former is stronger than the latter.
"correct" clearly grades.