You mention clearing immigration at ATH but both your incoming and outgoing flights are intra-schengen so there is no immigration to clear. You will arrive and depart from the same gate area with no need to even re-clear security. There's no way you can plan for a delay on your VIE-ATH flight of course, but you will have LOADS of time if it is not delayed. Even if you deplane at a remote gate and take a bus to the terminal, you will be at your departure gate no more than 10 minutes after stepping off your incoming aircraft. ATH really is that efficient now!

EDIT: Ah, I missed the fact that you have to re-check luggage. In that case it will take a little longer - you need to exit, re-check and re clear security. Still no immigration and you should easily make a 1hr55 connection with time to spare for the lounge. I see where you're coming from though. I would probably just book the A3 flights and know I could relax.