I was only referencing the fact that the individual user data appeared to be correct in one view, even though the session length distribution chart was way-off. Had it been off for all users, it would be a big problem, but only affects the first session (See my edit above).

I agree cohort analysis is useful, but not particularly difficult to capture and chart on the server side for web apps, or mobile apps with a server back-end. For SPAs or hybrid or mobile apps you need a facility to capture client side events, which is where something like Amplitude really adds value.

It's one less thing to build or run, but if it's hamstrung by limited reporting, free isn't really free - you have to pay to unlock the value of that event stream.