OK, this makes sense, given the save bonus.
There may be some gray areas I'm not considering, but this doesn't seem too bad.
One consideration: a Mage Slayer will receive 10 feats (5 bonus, 5 regular) after gaining Dispelling Strike; if all are spent on a given elemental dispelling, how much damage does it do per level? I'd suggest capping at d12/level, but you could also expand it to 2d8, 2d10, etc.