I would totally agree with your reasoning - if Satan did not exist.
How is it that Satan came to exist (becoming the 'baddy') in a heaven that was apparently perfect (before he - so we are told - got a bit above himself)? And once that happy event occurs, to which you look forward, when Satan, Death, and Hell are cast into the pit, and God wipes away the tears from the eyes of all the 'saved', and the new heaven and new earth emerge - what is stopping any uppity individual, angelic or otherwise, from stepping out of line again? Is God going to start inserting a few modifications into the 'free-will' scenario?
You see, your unfolding apocalyptic drama really has no ultimate denouement, since its premisses are flawed from the start. You wish to argue for free-will. Satan had free-will. All 'redeemed' souls ought to have free-will. Which then presents us not with a linear drama and its culmination, but a never-ending cycle of the potential to rebel against the status quo, thus invoking Old Nobodaddy's wrath.