In-wall tank can get the drain above the floor. Creative framing plus the additional pitch will get you over that beam. I've seen them used in concrete floor-condo construction to move toilets w/o moving floor drains/penetrations.
IMHO plumber is taking the easy way out with an AAV. We've used them in a basement, but on the second floor he should either cut in a new roof boot or tie into an existing vent. Minimally have him put the AAV in the accessible attic space and not a vent in the wall.
https://terrylove.com/forums/index.php?threads/toto-wall-hung-outlet-pipe-slope.69960/