I haven't dispelled magic and had it work once yet at 50 and it's mastered. Look at that log of Klemsor vs Thulgan and see how many times HE dispelled and had it fail. Tell me a Giant is THAT hard to dispel?
Dispel works fine. It's a slightly harder to land due to it's power. But it can be landed.
If you cannot land it, it's cause you are not insisting it.
Spells are not skills. Spells will be saved most of the time. Spells will be very difficult to land on a prepared opponent.
This is where player skill comes in. Recognizing the suit of his opponent and it's weakness so that you use the spells that are most likely to land.
On Klemsor, although uncommon, nothing prevents someone from getting enough saves to nulify their saving penalties.