the SOTC may seem to have more damage, but it actually has less DPS than the vampire knives. the main projectile, which lacks homing, deals roughly 64 damage. it then splits into 2-4 tiny eaters, which deal roughly half that. so, each one (we'll average it out and say there's 3) deals about 32 damage. 3x32+64=160 damage per click, without defense or criticals.
vampire knives deal about 29 damage each. it can shoot 4-8 projectiles, so we'll average that out to 6. if each projectile deals 29 damage, then 6x29=174 damage per click, without defense or criticals.
so on average: 160 SOTC damage per click, 174 VK damage per click.
now, if each of them shoot the least number of projectiles:
SOTC: 2x32+64=128
VK: 4x29=116
and if each of them shoot the maximum number of projectiles:
SOTC: 4x32+64=192
VK: 8x29=232
now, if we combine the totals of all of these:
SOTC: 480
VK: 522
and the vampire knives have healing, but the SOTC doesn't. also, the homing of the SOTC only works if the main projectile hits something. if it flies off into space, it won't home. also, each projectile might home into a different enemy, and deal less damage. however, the vampire knives spread, so can hit many different enemies and at short-medium range(i.e, the size of the screen) can be much more effective. and all that's without ichor(crimson) and cursed flames(corruption).