Well. I have pvped for a long time on my fire myth ice and balance. I have at one point been 1400+ warlord on all of them. Loremaster is a VERY powerful spell but it is surely not broken. Every class seems to have a cheap trick up it's sleeve. Whenever i go up against a balance on my fire i fill my sideboard with balance dispels and counter-act Loremaster and savage paw by applying early game pressure with fire elf, power link, and infection. This eventually leads to pips leading in my favor because of the amount heals needed to survive. In conclusion, I think it is powerful but not unbalanced.
When this spell was first released, I was under the impression it was over Powered. After watching it spammed over and over, I think the initial shock of the spell has worn off. Now, most expect it and pretty much ignore it, as the -35 accuracy seldom causes a miss. The -20 weakness seldom stops anyone from attacking, they just use a smaller attack.
I have noticed that many have crafted this spell or got it from Loremaster. Many non balance schools have designed their gear around this spell, so they can hit hard with it. So it's not just Balance using this spell anymore, lots of schools are using it. Still, I find it a nice adder, but nothing that is simply overpowering.
For a while now, I have seen a shift to the new 3 pip transform spells (can't remember the names). They can be enchanted, and the life spell leaves behind two items, just like Loremaster. If you have a lower pip percentage, lets say 85 or below, these spells are a great addition. I would almost say overpowering at times.....