Some of the DNN web pages I visit have large viewstates like over 40k even though the web page doesn't have any forms. One of pages I visited today had a DNN copyright of 2015 so it's one of the newer versions which should have the performance improvements with the smaller viewstates. I am guessing a module is probably causing the large viewstate. Large viewstate have a negative performance impact specially on mobile devices. If you're a DNN site owner, be aware of the viewstate size and see if you can minimize it. Browsers have extensions which display the viewstate size. For example there's Size Grabber for Chrome. Search your browser's extension/plugin library site.

When DNN goes to pure MVC, this issue will be gone as Viewstate is a ASP.NET WebForms only feature.

Yes but if  you don't have form elements which are used for user input, the viewtstate will still be small. Most of the form elements are hidden fields in a plain vanilla DNN page.  Dnnsoftware.com home page is 112 bytes when logged in, 136 when anonymous. A tiny difference so what's the impact if you're logged in or not?