Well done in making this point #1, this is absolutely 100% true.
Yes, they were overpowered; but we believed it was justified as they cost so much time, dark elixir or gems.
Now, the value of that time, dark elixir or gems is a mere shadow of it's former self. Yet cost to upgrade, time to upgrade are unchanged - and neglecting to reduce regeneration actually makes them slower to regenerate HP per minute.
That is why we are all frustrated, we paid and farmed hard to get overpowered heroes - something we felt was worth the high price / time.
You MUST provide relief on that high price / time to justify the lower stats.
Frankly, I have NO INTEREST WHATSOEVER to ever upgrade my king as a result of this update. The time, cost & effort is absolutely not worth it. I will upgrade ONLY my queen from this point, and even then will at a slower rate - no more gem time or boosted to get the dark elixir.
We are not idiots, we appreciate re-balancing the game; we do not appreciate our past and future hero investments offering so little value.
Now the hero investments offer to little, costs and time need to be reduced to match. You can not legitimately claim they are 'balanced' while leaving this element unchanged.

