Despite your affinity for geometry, geometric fonts are the exception, not the rule. And even geometric fonts often have tweaks that make them less "perfect" geometrically but look more correct. https://en.wikipedia.org/wiki/Sans-serif#Geometric
I can understand the "near-perfect" circle, but wouldn't you agree that the (mis)alignment of the green and red arcs' edges feels wrong? Not about typography/legibility, but about the balance of lines. Interestingly, in the Futura font, which is quite similar to Google's Product Sans, the top line of the G extends a little further, so that its edge would have lined up "perfectly" as I would have preferred. For comparison: https://qph.ec.quoracdn.net/main-qimg-4c522c183600dbc2ede9aa...
A short video that demonstrates the intention of the lines: https://g-design.storage.googleapis.com/production/v6/assets...
It came from this article, Evolving the Google Identity (https://design.google/library/evolving-google-identity/) under section "Google G Construction".