An alternative for "big" in the phrase "big proponent"?

Solution 1:

Staunch is good, as mentioned above. It implies that you will continue to propound the matter, even in the face of adversity, as would stalwart. (The difference is that stalwartness derives from a firmness in character; staunchness is a measure of one's adherence to a specific belief. You can be stalwart in general; you have to be staunch about a particular thing.)

A major proponent is a person who stands out as being significant in the community, as in "Obama was a major proponent of health-care reform" -- not just that he really advocated for it, but his advocacy was effective.

A vocal proponent makes his feelings known.

A passionate proponent gets emotional about the issue.

Someone else suggested vociferous, but that has a strongly negative tinge. People who vigorously advocate a position you disagree with are vociferous.

Solution 2:

You are probably looking for staunch. It is a widely used adjective to mean big supporter.

She was a staunch proponent of human-centered design.

M-W:

staunch adjective

: very devoted or loyal to a person, belief, or cause

She is a staunch advocate of women's rights.
He's a staunch believer in the value of regular exercise.