And then one leak in plaintext compromises all of your accounts because a targeted attacker is presumably smart enough to understand what you did...

To make it a bit less conspicuous, take the third character (or something) from the service name and put it as the fifth character (or something) in an otherwise long random string. This will look like a random password... until someone gets two or more passwords made with this strategy, then it's pretty easy to find out the strategy.

How is any of this easier than using a password manager??

You only have to remember one password, the strategy is the same for all passwords, replace the fifth character (for example):

google: mojko2if6bibe78

youtube: mojku2if6bibe78

yahoo: mojkh2if6bibe78

Note that I don't advocate this strategy for high-security applications, but for throwaway accounts that you might want to access when not having access to your password manager it might be useful.

I should clarify, there should only be a pattern like that for the many frivolous services, and a different password for financial medical etc.