Google Play Games usernames expose email prefixes by default?

I noticed something odd with Google Play Games: when you create a profile, your default public username is just your email prefix (the part before @gmail.com).

For example, if your email is coolguy123@gmail.com, your visible username becomes "coolguy123" by default. Most people never change it, especially casual users or kids.

Because of that, when you look at public leaderboards, you can easily guess full Gmail addresses just by reading usernames. It's not a data breach, but it does feel like a privacy oversight that makes email guessing way too easy.

Is this something that should be reported? Has anyone else noticed this? Wondering if this could be exploited or if it’s just a harmless default.