The math doesn't support you. Corruptor damage scale is 0.75 vs. 0.65 for a defender (i.e., 15.4% more damage). Assuming the defender has a 30% -resist debuff while the corruptor has 22.5% (i.e., 33% more -resist), Even with the defender's 33% higher debuff, it can't make up for the lower damage scale. The corruptor does 8.73% more damage before scourge is factored in.
Defender: 0.65 x 1.30 = 0.845
Corruptor: 0.75 x 1.225 = 0.91875
On top of this, corruptors get a higher damage cap (500% vs. 400%) and can skip the tier 1 blast.
That said, of course a blaster will out damage a corruptor. It's not even close.