Yup, I leveled the gem up to 28. And I find the build BORING. Fifteen minutes and I'd rather do anything else. The damage really sucks and it takes forever to kill even basic minions. Also, I play exclusively solo.
... what weapon are you using? You should be melting through enemies. I leveled a wizard 1-70 in about 4 hours -without- a gem of ease, just using a regular socketed weapon with a bigass ruby in it. A level 70 weapon should put out even more hurt.