Doesn't Google OWN Niantic? So now Google has access to our Google data? Don't see the issue.
2. The security risk isn't that Niantic is going to turn evil, it's that Niantic becomes an access point for other (evil) hackers.
Even if they were still owned by Google, a compromised phone with Pokemon Go has a nice juicy access token with admin rights to your account to siphon off.