Surge the Tenrec is one of my favorite characters in IDW Sonic. I love her energy, her raw anger, her punk aesthetic and the way she rebels against the purpose she was designed for. She’s fresh, unpredictable and has her own identity.
That said, she’s not quite a spiritual successor to Scourge. She ticks off several boxes - green quills, evil foil to Sonic, even a similar name - but really she’s more of a thematic cousin.
Scourge’s whole thing is that he’s a version of Sonic who embraced his worst qualities. He’s a dark reflection, quite literally what Sonic would be under different circumstances. Even his personality matches what Sonic might be like if he were a terrorist.
Surge on the other hand was never a reflection of Sonic. Anything she has in common with him was conditioned into her. She’s a convergence rather than a divergence. A closer Scourge expy doesn’t necessarily have to be Sonic from another world, but there should be some point where they were effectively alike.
I know not everyone will agree with this and that’s okay. I just wanted to share my take.