Well, I'll assume your answer was directed at me, thank you for that. I love to exchange ideas.
What you have mentioned could have multiple reasons. First and the most important one is that people don't want to waste their time with healer profession, it's literally a waste of time. Anyone can just join a tallaar's halls after reaching level 7 and increase their executioner profession with ease, but such thing is not possible for healers. They will have to wait for people who have injuries yet one has to be either the target of someone (like an executioner who often comes to their land and executes him to get levels) or has to be very clumsy so he/she dies to mobs over and over again to get injuries. The only people who have injuries all the time are naked hunters and thx to the cuisses bezels, they mostly get level 1 and sometimes level 2 injuries.
It's hard to increase it, yes, but it's not expensive nor is the cost high, not on any occasion. Because since it's a service, you can just tell people to buy their scrolls themvelves or charge them when healing them. By little to no loss of money, you can increase your healer skill fast. The only problem here is to find people with injuries.
Yes, I agree with you on the point of healers not healing themselves but healing others as well. Then again it's a quote unquote productive profession, not a destructive one. The goal of executioner is to give injuries but the goal of locksmiths and healers is to help people.
So in conclusion: It's a logical balance.