Any reputable service allows changing email addresses. For less important services like Amazon you can use an email alias. Tutanota and Proton are nice email providers whi do not read the content of your emails and and not scan files.
> My email address is, of course, the primary means of communicating with me other than phone.
If you have a phone, can't you just install a messenger? Session does not require a telephone number nor a smartphone, I think.
> I also use Sign In With Google on dozens of the above accounts, so they are a definite dependency on the Google account.
In your Google Account settings which accounts use Sign In With Google. Go to each account and change authentication to email and password wherever possible.
> I own an Android phone and a Chromebook. I operate 3 personal accounts, and my employer relies on Google as our primary business platform.
Does not prevent you from using a secondary email for your personal important stuff like government and financing.
> My Google Calendar and Tasks are my sole method of scheduling everything I do in life, from daily tasks to events I attend and everyone's birthdays.
> My Google Contacts contain all contacts of everyone I know and is the sole repository of that data.
Should be exportable as ics files I think. Make at least a backup once in a while.
> Google Docs and Sheets are my sole word processing and spreadsheet apps, which I use to great effect for writing letters, managing household, etc. etc. I know them like the back of my hand, and I also use them every day for work.
Get an offline editor like LibreOffice. Online editors are crap when your internet connection is off or need to make a ton of content.
> All the photos I've ever taken since 2015 are stored only in Photos. Not many, of course, but some I'd miss.
You can download them for offline use, make a backup and then print out the ones you really care for.
> I'm increasingly using Wallet and GPay for financial transactions and event tickets. I even hear tell that my jurisdiction is putting driver licenses on Wallet now.
If you use GPay, it is even more important to not have any content stored in your account. See the case of a father sending his doctor a picture of his son for diagnosis. It was falsely recognized as child porn and the father had no way to get back the account. If your account gets suspended, you are out of luck.
> So could you rephrase your advice to me please? Which $20/year service replaces these apps, and permits easy import of all my data from Takeout?
> If someone used 365, would you demand that they GTFO Microsoft and junk their Windows systems? What should we run? A PDP-11?
Noone said to nuke your Google account. In fact you're being very passive aggressive despite not having made any effort on researching alternative apps. Don't tie your whole offline and online identity to one provider who doesn't care about you except for your (and people close to you) money and data.