Healer needs a buff, nevermind Valkyrie.
Healer is almost useless for everyone with TH lvl 8 and above as everyone who knows how to play this game will have well defended and developed air defense. For farming low level players, the healers are useful as the weak air defense can be taken out before deploying a healer. But for everyone who is attacking for say a well developed base, healer is just a waste of elixir and 14 space.
Healers are absolutely useless for clan castle and when you take it to battle. They need a huge boost in dodging those missiles. My suggestion on how to improve them is by setting up a system where they would have 1 in 3 chance of getting hit by the air defense. With that it will all depend on luck and may give them a better chance of surviving a bit longer.
I don't agree with the problem
I find healers work fine with if you make the necessary troops combinations - against AD's that is. They are definitely useful against TH 8
What I find is once your trophy count is high enough, people will use black air-mines. 1-hit and your healer is toast.
Aside from that throwing in a few minions or balloons can draw fire away from the healers. Played right you can still have a pretty good go at 50%. Still that one shot kill is hard to get around.