I have a Yahoo Japan account and find this incredibly frustrating. Obviously they've measured it to be better on average, but if you already have a password manager, it's just an extra hurdle and waste of time when logging in.
This effectively overrides all of the improvements in password managers, especially OS-level ones, in recent years. On iOS, for example, the system suggests a strong password on account creation and then autofills very quickly and easily both on the web and in apps, so it's secure and you never have to think about it. But now with this change, you don't even have that option and you always have to wait for the email, open your email, click the link to go back to the app/site, and then go back and delete the email.
This effectively overrides all of the improvements in password managers, especially OS-level ones, in recent years. On iOS, for example, the system suggests a strong password on account creation and then autofills very quickly and easily both on the web and in apps, so it's secure and you never have to think about it. But now with this change, you don't even have that option and you always have to wait for the email, open your email, click the link to go back to the app/site, and then go back and delete the email.