hey Irish, look at what I bolded above, you listed one of the main advantages in your own post. That is a pretty big advantage, it let's you save potentially A LOT of elixir.
I could use full 11 dragon raids on weaker bases in gold league and over half of them would survive. It would cost me only half the amount of time to recover the 4-5 dragons that DID die and I would be saving a ton of elixir that way. this is what you call OVERPOWERED.
Another huge advantage is the fact that this would let you raid a lot more often since build times would become shorter. Supercell makes MONEY off of people spending gems to speed up their barracks. If this were to be implemented, a lot of people would be boosting barracks less or never.
Along that same train of though, if your armies build faster, you can raid more efficiently to the point that it would be very difficult to find collector raids for farmers, because everyone else would be attacking so much, they would be snatching up those collector bases, giving them 12-16 hour shields while you are clicking next, getting even more frustrated looking for that next collector raid.
These are huge advantages that mess with the equilibrium of the game.

