There's more to come off the heels, as well the heels are of different heights, but I think the biggest problem now is that your frog is not healthy. All the dead, crappy stuff needs to come off, the channel cleaned out, and let the whole length of the frog hit the ground to get blood flow going.
If the horse were to step in a shallow puddle of water and then walk on a dry spot the wet imprint of the hoof should be an entire wide circular band that does not have any breaks in it...that means the heel and frog should close the band, and then you should be able to see the entire frog. Only a small inner part in the shape of a 'U' (the front being the inner part of the 'U') should be 'dry'.
More development means more weight bearing is happening there. In turn that means the trim is not balanced.