What keeps being overseen is the amount of engineering to make reference counting perform in modern hardware, effectively overlaps with other garbage collection optimizations.

You probably wanted "overlooked" here. Even though "seen" and "looked" are similar in meaning, "overseen" and "overlooked" are not. This is a subtle but important distinction in English. https://grammarist.com/usage/oversee-vs-overlook/

Historically you could choose "oversee" when you would today use "overlook" or vice versa, but these usages went from archaic to actively disapproved. One remnant though is you would still use "overlook" in a sentence like "Atop the hill, the old castle overlooks the whole town".

It seems remiss of Grammarist to write an entire page without mentioning that.

At m.d.s.policy it was our view that Symantec management had inadequate oversight of Symantec's Certificate Authority and as a result on several occasions over an extended period an important oversight relating to the name validation procedures at CrossCert, a Korean business authorised by Symtanec to issue on their behalf - occurred without being detected by Symantec. This definitely resulted in undetected misissuance.

As a result of our efforts to fix this problem Symantec sold their entire CA business to DigiCert, and CrossCert became merely a reseller of DigiCert's products (including "Symantec" branded certificates)

This meant that now DigiCert's trustworthy management exercised oversight over all issuance of certificates from the new CA hierarchy even when the certificates had "Symantec" branding - while an oversight by CrossCert, such as failing to verify the identity of a customer, would no longer cause misissuance because DigiCert would independently use the Ten Blessed Methods.