Apple has not publicly explained the specific reasoning behind the new macOS 27 battery indicator or identified the designer responsible for it.
Alan Dye leads Apple's Human Interface Design organization, but there is no public evidence that he personally designed this icon or made this particular decision.
The change places the battery percentage inside the battery symbol.
Apple has not said that this was done to save space, reduce menu-bar clutter, or achieve consistency with iPhone, so those explanations should not be presented as facts.
The more objective question is legibility.
Apple's Human Interface Guidelines for macOS emphasize comfortable information density and note that Macs are generally viewed from about 1–3 feet.
Apple's Accessibility Guidelines emphasize adequate contrast, while its Typography Guidelines address readability at different viewing distances and conditions.
It is important to distinguish contrast from legibility.
An icon can technically have adequate contrast while still being difficult to read quickly because the text is very small, confined within the battery outline, and visually competing with the surrounding graphic.
Since battery percentage is useful status information that users commonly check at a glance, that makes glanceability an important consideration as well.
Your observation that the percentage becomes difficult to read from a normal working distance is therefore a legitimate UX concern, rather than simply an aesthetic preference.
It does not, however, establish that Apple has violated its design guidelines.
The most accurate conclusion is: Apple changed the battery indicator, but has not publicly disclosed the specific design rationale or testing behind it.
Apple's published guidelines give us reasonable criteria—legibility, contrast, viewing distance and information density, with which to evaluate the result, but they do not tell us what Apple's designers considered internally or why this particular implementation was ultimately chosen.