I mean, you can disagree, and run it that way, if you want to, in your game... but the lore as set out by the Avernus book is as I described. I can find you the relevant paragraph if you'd like?
A coin has three charges, and asking aquestion consumes a charge. Consuming all three charges frees the soul to pass to whatever afterlife would otherwise await it, as does shattering the coin. Burning it in an infernal engine destroys the soul by using it as fuel, but any other method of destroying a coin frees it - and that's counted as a good act.
I agree that drawing off energy *Seems* like you're eating the soul, but formally speaking, that's not what's actually happening, apparently... Perhaps the concept is that the energy you take from it counts as exacting its pennance or payment, rather than actually devouring the soul itself?
Here we are (bolding mine):
Soul coins are about 5 inches across and about an inch thick, minted from infernal iron. Each coin weighs one-third of a pound, and is inscribed with Infernal writing and a spell that magically binds a single soul to the coin. Because each soul coin has a unique soul trapped within it, each has a story. A creature might have been imprisoned as a result of defaulting on a deal, while another might be the victim of a night hag’s curse.
Carrying Soul Coins. To hold a soul coin is to feel the soul bound within it — overcome with rage or fraught with despair.
An evil creature can carry as many soul coins as it wishes (up to its maximum weight allowance). A non-evil creature can carry a number of soul coins equal to or less than its Constitution modifier without penalty. A non-evil creature carrying a number of soul coins greater than its Constitution modifier has disadvantage on its attack rolls, ability checks, and saving throws.
[...]
Using a Soul Coin. A soul coin has 3 charges. A creature carrying the coin can use its action to expend 1 charge from a soul coin and use it to do one of the following:
Drain Life. You siphon away some of the soul’s essence and gain 1d10 temporary hit points.
Query. You telepathically ask the soul a question and receive a brief telepathic response, which you can understand. The soul knows only what it knew in life, but it must answer you truthfully and to the best of its ability. The answer is no more than a sentence or two and might be cryptic.
[...]
Freeing a Soul. Casting a spell that removes a curse on a soul coin frees the soul trapped within it, as does expending all of the coin’s charges. The coin itself rusts from within and is destroyed once the soul is released. A freed soul travels to the realm of the god it served or the outer plane most closely tied to its alignment (DM’s choice). The souls of lawful evil creatures released from soul coins typically emerge from the River Styx as lemure devils.
A soul can also be freed by destroying the coin that contains it. A soul coin has AC 19, 1 hit point for each charge it has remaining, and immunity to all damage except that which is dealt by a hellfire weapon or an infernal war machine’s furnace (see "Soul Fuel").
Freeing a soul from a soul coin is considered a good act, even if the soul belongs to an evil creature.
Hellish Currency. Soul coins are a currency of the Nine Hells and are highly valued by devils. The coins are used among the infernal hierarchy to barter for favors, bribe the unwilling, and reward the faithful for services rendered.
Soul coins are created by Mammon and his greater devils on Minauros, the third layer of the Nine Hells, in a vast chamber where the captured souls of evil mortals are bound into the coins. These coins are then distributed throughout the Nine Hells to be used for goods and services, infernal deals, dark bargains, and bribes.
