You can trigger events with JavaScript and choose whether they affect bounce rate, so you can manually trigger an event when the user scrolls down, clicks something, spends a few minutes on the site, etc. So your problems with the bounce rate metrics are just not true.
Also I saw you mention it doesn't track returning users, that's not true either. I can actually see insights into how many users return month after month, and it'll tell me what my activity is per channel and if one channel outperformed others, so it's pretty powerful in this regard for a free platform.
I skimmed it but from just reading those it sounds like you should try to get better familiarity with Google Analytics and talk to users to see what their main pain points with existing platforms are, as well as establish more concrete value propositions. Google Analytics is free after all, I'm not convinced yet to move to a paid platform that tries to address problems I'm not experiencing.