But the issue with that is you say STN has a cap of 35m and eventually up to 44.5m, you do realise that the MAN TP is aimed at smoothing out the process to enable the 55m passenger cap there (it's technically capable of 55m now, but would not be a pleasant experience, the MAN TP is to give the terminals that breathing space).
As said, MAN is growing at a faster rate than STN, and MAN can still draw on a far greater airline diversity, whereas STN is very heavily loco dependant.
All I'm saying is that yes, it's entirely possible for STN to regain its 3rd largest spot, but, it's not the dead cert you seem to think it will be. Don't forget, MAN and STN is owned by the same company now, and they have grand plans for both airports.