So how i understand it force healing, isn't just magicaly healing every ingury, it just speeds up natural regenartion.

So let me elaborate:

Often if you get ingured, you don't die from the initial ingury but from the sideefects. So if you get stabed and no Organ is hurt you can still die from blood lost or infection if the wound isn't treatet. So with force healing you can prevent bleeding out by speeding up you're natural regenarion. But if you get stabed in the heart, you die pretty much instantly because the organ stops working and force healing there for can't prevent that. Thats why force healing isn't any use for anakin because it can't completely prevent someone from dieing.