onstage my arms look small.
onstage Vince Taylor's arms look huge.
side by side my arms look as big as Vince's
You also have to take in the detail of the arms, and shape---V taper...a great V-taper/small waist makes a good size arm look bigger.
In terms of detail, Phil Heath is a good example---during his Rookie yr, his arms were just as big as Darrem's, or maybe it "seemed" that way, due to detail.
Your arms are vascular, thus giving a image of size as well.