Mineshells have a delayed fuse what let it explode after it penetrated the surface it hit (even if just a bit).
Normal HE explodes on impact on the surface. The difference of the damage dealt can be easily portrayed by letting a firecracker explode on top of a price of snow or buried into it.
The result is much larger punctual damage (big ass hole) what is catastrophic on airplanes but rather pointless on soft targets, where the splash damage of standard HE is much more effective.
The effectiveness of the Mineshells is much more related to how and when it blows up and fragments don fly far around inside of a wing, so more chemical power is the better choice.
Besides, if the mineshells would be less effective than simpler HE designs from the time, why did other nation copy it, on for example the ADEN cannon?