You think FS2004 is bad, you have'nt seen FS2002, to go from FSX to that is amazing. I'm not doing company flights on FS2002 (yet) but it's still amazing to see the diffrence.
FS2004 is, under the hood, FS2002 which had major code improvement over FS2000 but was not as much of an overhaul as FSX was. Since FS98 the basic code has remained unchanged. FS2002 did add new protocols for gauges, the .xml gauge format, and most importantly the 3D Virtual Cockpit. But both FS2002 and FS2004 remained 100% backward compatible with the FS98 era gauge format thus allowing people to mix and match aircraft, sounds and panels. FS2004 did add improvement in the FDE department. From FS2000, FS2002, and FS2004 we slowly got further away from the ambiguous .air file and more information was placed in the easy to edit and easy to read aircraft.cfg
To go "back" to FS2002 is a misnomer, yes there were a few improvements over FS2004 and FS2002 (MS had to justify a $60 price tag for what was basically an update) but most of those updates where surface deep. What FS2004 did, was add content while improving overall performance of the simulator. To choose to load FS2002 over FS2004 would IMHO be like loading Windows 2000 over Windows XP. Sure you could do it, but why? You are going to get less content, and slightly lower performance. To go back to FS2000, you must be nuts. Some of us are trying to forget that nightmare and are only haunted more by FSFW95.