I don't really know. I'm not an advocater for printing effects that would prevent many decks from functioning, unless the decks are not healthy. To be honest, I don't really feel like energy discarding effects are overly unhealthy, a you can just add more energy in your deck or run low-cost Pokemon and/or energy accelerators.
You just explained
why easy discarding of Energy is unhealthy for the game; remember you get
one manual Energy attachment per turn.* We currently have
Crushing Hammer, an Item which can discard any one Energy card and is "tails fails". That isn't good game design: the coin flip doesn't properly balance out the card and we've seen that over the last few years since it came out. Either the format is such the card isn't good enough
or the card becomes amazing as it interacts with other things.**
Enhanced Hammer isn't much better; it helps balance out the overpowered Special Energy cards, but as it punishes
all of Special Energy it would be better to just
not have the overpowered ones. =P If you think no Special Energy cards are overpowered, that is fine. In that case it still stands that a precious Special Energy card, which is hard to search out from the deck, hard to reclaim from the discard pile and which uses up one's manual Energy attachment for the turn should cost my opponent
more than a simple Item.
Team Flare Grunt and
Xerosic probably
are more or less balanced in and of themselves: once per turn Supporter usage traded for once per turn Energy.***
I'm not sure if
Eco Gym is the best response, but it might not be a bad one. The decks you mention aren't prevented from
functioning, they are preventing from dominating and reducing the amount of the card pool that is tournament viable. Right now to be competitive you either need Energy acceleration (often with Evolution acceleration), low Energy attacks or
both. There may be some exceptions of which I am currently not remembering, but they would be just that: exceptions.
*Decks that get multiple are already "bending the rules" and if they are too powerful, that is a separate issue with that card (discarding effects shouldn't be used to balance them out).
**Even when it "sort" of seems balanced (some decks use it, some don't) it is an additional, binary result bit of variance so instead of winning with skill, you're relying on even more "luck". That may not sound too bad but please remember that long time players had to deal with an incredibly frustrating format where Pokémon Reversal (with help from the rest of the competitive card pool, of course) was deciding games. While there was some leeway in general the people who won tournaments were the ones that flipped well when it mattered.
***Though VS Seeker and Shaymin-EX (ROS) are allowing them to be more effective than perhaps they ought to be.
