The fact that platformClient.PureCloudRegionHosts['us_east_1'] returns mypurecloud.com is expected/normal.
When invoking client.setEnvironment(environment), the SDK sets two path: one for authentication (adding https://login. prefix to environment), one for api (adding https://api. prefix to environment).
I have used the sdk few days ago (version 135 - out of nodejs) and didn't notice such issue.