“Check-circle” is exactly the amount of information that the able reader has. Sight-deficient users are as much used to those weird words as able users are used to unintelligible icons.
If the image stands alone such that sighted users must parse it, then your logic is correct. But if the image is merely decorative due to adjacent text such that sighted users gloss over the image, aria-hidden affords users of screen readers that exact same efficiency instead of wasting their time.
In other words, eyes can skip over decorations without the developer needing to flag them as such, but audio can't auto-skip.
All text being skipped unless the author tags it for inclusion doesn't seem like a failsafe default, assuming that excessive information is generally preferred over insufficient information.
No the reader has "account_balance_wallet" (no dashes). It will read as "account_balance_wallet account balance wallet."
It would be trivially easy to use ARIA attributes to indicate which span is the icon's label. Not something most people consider, but this is Google. At least they have an accessibility icon?
No. A sighted user can perceive the placement of the icon within its context, e.g. a checked circle within a row in a table, and deduce that it represents confirmation of whatever information the column of the table represents in the context of the row. This information is not available to a screen reader user unless the visually hidden text makes it explicitly available to them.
By the way, your comment shows an ableist bias: an analogous assumption would be that a person who cannot walk is content because they are used to a wheelchair.
