I know after TH 8+ and definitely at TH9+, people pretty much stop using healers as the amount of space they take up in an army does not justify how easy it is for a healer to be simply destroyed by triggering a seeking air mine.
Because healers only heal ground units, the majority of one's army is going to be ground with a small number of healers mixed in. This means that the only air units that are going to be in the army mix will be healers and these will be the only targets eligible for those seeking air mines to target. Considering there is already a lot of anti air towers covering most of the base, it is already difficult to use healers well at higher TH levels. Add to the fact that after taking out the air defenses, a well designed base will usually have some seeking air mines near by which will take out any healer.
If healers only triggered red air bombs, I could see them being viable again in armies but if they are going to be vulnerable to seeking air mines as well and can only heal ground units they are pretty much a waste of space in an army.





