In the market...you expressly buy the resources with energy.
Only in the galactic market.
In the internal market, the use of energy is an abstraction for non-permanent infrastructure industrial activities that don't rise to the level of a district. There's no external, or sometimes even internal, alternative source of resources, and the ability to convert energy is limited by the 50-or-less unit limit regardless of how large (or small) your economy in.
This is the in-game/game mechanic separation that you're not addressing. In the game setting, the only market that actually exists for all empires is the galactic market, which may not even be established until nearly a third of the game is complete, for which energy is indeed the only currency. In the game mecahnical sense, the galactic market is one of several economic systems, each with there own currency.
You have approached this as a game mechanic currency issue, but are arguing it on grounds of an in-game currency issue, without addressing the other mechanical currencies.
A: getting to 50 consumer goods from trade value before you meet a neighbor is...an edge case.
Edge cases are what game mechanic has to consider. You are proposing a game mechanic, are you not?
B: No matter how much currency, you can't buy more stuff than a market can produce. In this way, the early restrictions make perfect sense...and don't make the thing buying those things not a currency.
I didn't say it wasn't a currency- my position is that mechanically the game has several currencies- I said that your empire isn't actually buying things with with energy in the internal market phase, on grounds that the internal market is an abstraction, not a literal market.
If you want to argue internal market energy is a transaction with a party rather than a mechanical abstraction, you have to address who, exactly, is selling alloys to the Gestalts or the state in non-private-economy empires, and why they can supply both unlimited commodities if you have the energy, and yet only provide 50 units at steady pricing no matter how large your empire is.
Until you can do that, you have not established that there is an in-game internal market (as in, an organized marketplace in the setting) in the first place.
C: I agree that we don't use energy to buy most things. That's part of why I want to STOP USING IT TO BUY THINGS IN THE MARKET. Because its a bad currency.
In-game or as a game mechanic? I'd disagree with both, and find your case for a trade value currency even less compelling on in-game grounds.
In in-game terms, trade value doesn't even make sense as a medium of exchange because it's not even a medium. It's an abstraction of private or organized economic activities, not even a currency on its own terms, and activities can't be stored or traded or transmitted. Storing tons of energy onto sci-fi batteries and shipping them around the galaxy in exchange for return shipments of other things at least makes energy a sensible form of stored value at relevant scale.
As a game mechanic, energy already works well as an inefficient-but-available conversion system for non-abstract resources, which exists to- among other things- help protect the player and the AI from the consequences of economic imbalancing by letting them convert one resource into another. Any system in which you can sell minerals/food/even energy for TV and then using TV to buy the other things is doing the exact same mechanical function. TV is just a relabeling of energy, while energy and all energy-related mechanical systems would have to be redeveloped and re-balanced around the TV conversion baseline.
That's what commodities are.
And commodities can be used as currency, yes.
The galactic market is composed of nations who have no interest or use in Trade Value? I disagree. The market is composed of the nations in the galaxy, most of whom generate trade value of their own, and I've already made the point that gestalts who don't have...economies...on the inside of their borders would still reasonably have an interest in Trade Value as currency, because anyone would have interest in currency if they have interest in any of the things it can buy.
This is post-hoc rationalization to justify changing the mechanics to fit a personal model, not basing your model around the mechanics that already exist. The fact that you have to qualify with 'most' is where the proposed system stops being a generalizable system as a versimilitude game mechanic, because the game needs a system that makes a minimum level of sense even without non-gestalts.
As it stands, the system you're advocating for one in which five gestalt empires meet and form a galactic community and improve economic integration, they... all decide to create clerk jobs to create a currency none of them actually have the ability to use except to trade to others who likewise have no ability to use.
Ultimately, I guess we don't agree on what the words currency or commodity mean.
Feel free to try and establish a workable definition, then, and distinguish whether you are talking in gameplay mechanics or just rebranding energy as a name for the same systems.