I have email addresses under Outlook (old personal account), Gmail (study provided email), Exchange (work) and Proton (main personal account). I also actively use the calendar feature in my client, which is sync'd up to my Nextcloud instance.
Just having it all under Thunderbird is so convenient and it feels more private. It's also an entirely consistent UI between accounts
Its pedantic and distracts from the real conversation happening. I've always considered "stock" to mean how the device ships from the factory (that's how the term is used in the automobile world), whereas I would think it fair to consider AOSP a standard, it's something you can compare other ROMs against.
Regardless of mine or anyone else's opinion, we're just ultimately wanting to talk about how GrapheneOS is much closer to the clean and uncluttered experience AOSP offers