The point is that almost every Blaster secondary has a strong Damage buff, and these numbers are also higher for Blasters. And yes, Defiance gives a significant stacking damage buff almost all the time. We aren’t debating the merits of Sentinel vs Blaster, simply evaluating why a power might be implemented differently for the two.
However, I’m also not completely sure those 218 and 219 numbers are accurate, but I don’t have toons to test with.