I could see that. Poison and Trick Arrow can reach higher -res however it takes two powers to reach it. If Defender Tar Patch was maybe -35 res it would be a respectable go-between if the others were kept at -30. I don't have the formulas they do however so...
EDIT: Slowed Response for example takes two powers to reach -36 res on a defender, TA is -40, Poison can reach a whopping -65 on one target while the rest are -45, Pain Dom is -30 only, Rad has Enervating for only -30, Sonic can hit -60 with two powers, Nature is only -25, and I think Sleet and Freezing Rain are -30 if I am not mistaken