What makes you think the compliance burden is any different for self-hosted analytics vs third-party analytics? You're the data controller in both cases, your obligations for consent/interest, disclosure, access requests, etc are all the same. Google Analytics has a DPA where they guarantee they meet their GDPR obligations relating to your data, and Google is a member of the US-EU Privacy Shield, which takes care of your obligations with respect to transferring data outside of the EU. If anything, hosting your own Piwik instance greatly increases your compliance burden and risk of a costly breach, as you'll be collecting and storing much more personal data than Google does, in a less secure environment -- Google Analytics is mostly aggregate/sampled data, and supports IP anonymization at the edge before any processing/storage is done.