Stardust and candy cost of powering up

I really wish they did something like that...It makes completely sense to me and to a lot of people. I don't like how the game prevents you from powering up the mon you like just because it has not the best stats.

Now all mon have a place in a gym, why not balance them a bit more with their powering up costs? No one will ever spend the same dust maxing out a Butterfree having Mewtwo, not gonna happen. But if Butterfree costs 1/4 of Mewtwo then someone may think about it and enjoy the game with different mon than the "top" tiers.

Not sure about giving back the dust tho, but agree with everyting else.

Just take the game as it is.
The "unpower" thing is NOT gonna happen.

No, what you are asking for is just the desire of a fickle player. It makes no sense.

As a trainer you choose which pokemon to power up either because of their usability or you fancy them. Luckily to us, PoGo is an evolving game and usability of pokemon changes over time with the additionon of new mons and abilities. The leveling system is well balanced. It's up to you how much do you want to invest in the new usable pokemon. They will eventually become obsolete in a years time as their predecessors. But that's your choice as a trainer, not Niantic's call. Even the opposite, I don't want Niantic to touch my pokemon, what I did with them is my call, not theirs.
For instance, your example of jolteon is a really wrong one. Jolteon has been the best electric pokemon with a huge difference. Many of us have maxed out our best jolteon and they gave us thousands of victories, plus the access to more powerful version of other moms (legendary birds, etc).
Work your ass walking, catching and hatching to power up your new favourite, but don't ask to destroy all the previous effort put into the game.

I work at catching Pokemon every day and have over 500,000 Stardust. I run into players at raids and they are always short of Stardust. They just go from raid to raid.

Niantic keeps Stardust rare so players will keep catching Pokemon, the original intent of the game.

No, it's a power creep which occurs in these types of games. Think about it this way, your dust is actually worth more because it is powering up more powerful mons.