I can confirm that any HTML portlet approaches calling the /niku/xog endpoint in Clarity for XOG requests is fundamentally different and free from the issues of the old xog.client action that ran all the processing (as both client and server on the backend) through the /niku/app and /niku/nu servlets.
So whoever said it does not have similar issues would have been correct about that.
The HTML portlet /niku/xog versions are no worse or burdensome to the server than using any third party SOAP tool like SoapUI, and they are fine (so long as they work - I don't know at which point you might cause the client browser to explode for example, but the backend load is the same as though any other client is connected and pulling data).