The new Web UI has gotten quite a lot faster since release. Mine fully loads in under a second now, with one more second for hangouts to connect. The Android app I have all the tabs disabled though, but I don't have any speed problems there either. Are you still experiencing the slow performance that were there at launch?
I claimed the new UI itself has improved quite a bit since its release 2 years ago. I'm not sure what that has to do with Gmail beta from over a decade ago.