Neonivek: Tell me, how does healing magic work IRL? Frauds take your money and leave town before you wise up.
In DF, we can and probably should make healing magic balanced against not having it, ie mundane healing. This is low fantasy, and having a few dwarves who can easily patch up any dwarves who didn't die within minutes of getting injured(and, if deployed into the field, many or most of those) would ruin both the low fantasy and the grittiness of DF, IMHO. Want that stuff? Make a high fantasy mod, once this stuff gets added it'll be easy enough. You disagree with my points? Fine, if I can't convince you here, I'm not going to make any ground. Let's move on.
If there's only one good choice, there's less of a game. There are many good choices among all parts of DF. While wax crafts aren't a viable export, stone, metal, and possibly even wood, bone, cloth, or leather crafts are, and with the right work a beekeeping industry can be useful. If healing magic is overly easy, say if it just takes a day of dorftime, it would make doctors less useful than beekeepers. After all, doctoring requires everything from time to lye to thread to potential labor, and has chances of failure, AND requires four or five skills, AND is rather limited in what it cures.
The problem isn't an issue of "easier vs. harder," it's about a single thing having the power to save your fort if used and to kill it if not. Imagine if every injured dwarf, from the legendary axedwarf with his arms amputated by a dragon to a hauler whose finger got broken by a flying boot, could be made very quickly good as new--not crippled, no loss of productivity, no chance of later death from infection or neglect. If you don't see the difference this would make, I'm not sure that we're playing the same game. For me, lots of useful dwarves would have been saved. Now, since we're Bay12, imagine what happens WHEN we give four or five clerics defensive training and steel armor before sending them into battle alongside the militia. The soldiers would be healed as they're harmed, and unless healers are given a conspicuous immunity to healing magic, they'll heal each other. Imagine an evil biome, but the corpses have metal arms and armor, quite possibly superior to your own.
You're saying that it's balanced if only one in a thousand can get the opportunity to throw their game off-balance? That's
luck-based balance, and there's a reason it's not listed under the "Good Balance" trope. It just means munchkinney people will spend a thousand times as long generating worlds and everyone else will be ecstatic when they get a healer, because it's rarer and more useful than even the king. That doesn't solve anything.
Alright, that seems to be everything, so I'll just repeat my case:
Healing magic shouldn't be the core of your medicine when you get it, but it shouldn't be worthless either. There should be situations where it's useful and situations where it's wasteful or even harmful. Maybe healing injuries requires inflicting harm on the healer or another. Maybe it requires valuable (to the player, not high-priced) reagents. Maybe it has harmful side effects, like stimulating pathogens as well as the healthy cells. Maybe it requires bargaining with a dark power. Maybe it varies from healer to healer. Whatever the solution, it must be done.