The star on its own is horrendous DPS, you need the blade to deal any significant damage, so Red.
You physically cannot hit the wall of flesh with a vertical weapon without it also being on your screen, so no safety here.
Star is a projectile (doesnt hit immediately), so you can actually hurt WoF outside of your screen while constantly moving forward. But it doesnt really matter if it is off screen or right on its border, my point still stands - you can keep safe distance most of the fight (the only exception is when WoF is on last 5% health and starts charging into player with insane speed).
You seriously inderestimate the star's dps. I would even say, the blade dps is not that important at all.
To prove my words:
Star has a delay of 40 frames, deals 44 base melee damage and usually hits 2 segments: eye (0 defense with sharpening station) and mouth (6 defense), for a total of (44 + 41) / (40 / 60) = 127.5 dps. Blade only hits mouth for (22-3) / (20 / 60) = 63 dps. Plus I might be dumb, but I dont know how to swing in the opposite direction of character's movement - its only possible for swords with built-in autoswing, like Night's edge and Muramasa. Neither Starfury, nor other swords like Fiery greatsword can do so, and you wont get even these 63 dps consistently.
Yes, 127.5 dps is not a lot, but its guaranteed and 100% safe. 1.5 minutes of going left side - and expert WoF is dead. And of course most of the time you have some good equipment - with molten armor, legendary modifier, wrath potion and all Lucky reforges you get
(44 × (1+0,17+0,15+0,1) × (1,04+0,07+0,05+0,2) × 2 − 3) ÷ (40÷60) = 250 dps, which is pretty decent (requires 45 seconds to kill WoF).
Starfury is easily the best melee weapon against WoF, I cant even imagine beating her with Night's edge or something else, its less effective and way more risky.