Once you have many accounts, URL matching (helping with phishing resistance) for autofilling and filtering may help as well. I swear some people on the Bitwarden forums have claimed they have 1,000+ account credentials.
Of course, a password book for recording strong generated passwords would be another method of keeping your passwords. There would be no wholesale infostealer theft. Not much estate planning is required, but there are also problems with backups for some people.
I started with using the same passwords everywhere, then continued with patterned passwords until I began having problems keeping track (not even that many accounts) when I started using a password manager (I never liked using a spreadsheet to keep track; too many chances to ruin multiple records at once). Once my passwords started leaking, I became too paranoid to even use the patterned passwords, resulting in using a password manager becoming completely entrenched. Once I needed access on multiple devices, Bitwarden became the go-to (since it's free).