No way should Moon be in the top 25. He put up average numbers once he wasn't in the run and shoot. As for the argument that he would have better numbers if not for the CFL, coulda, woulda, shoulda. The fact is he DID play in the CFL. Players are judged on what they did do, not on what they might have done.
Besides his first 3 seasons in the league, where are the average numbers (from 1994 and on)? Are you referring to 1996 and on, when he was almost 40?

Passing | Rushing |
+----------+-----+---------------------------------------+-----------------+
| Year TM | G | Comp Att PCT YD Y/A TD INT | Att Yards TD |
+----------+-----+---------------------------------------+-----------------+
| 1984 hou | 16 | 259 450 57.6 3338 7.4 12 14 | 58 211 1 |
| 1985 hou | 14 | 200 377 53.1 2709 7.2 15 19 | 39 130 0 |
| 1986 hou | 15 | 256 488 52.5 3489 7.1 13 26 | 42 157 2 |
| 1987 hou | 12 | 184 368 50.0 2806 7.6 21 18 | 34 112 3 |
| 1988 hou | 11 | 160 294 54.4 2327 7.9 17 8 | 33 88 5 |
| 1989 hou | 16 | 280 464 60.3 3631 7.8 23 14 | 70 268 4 |
| 1990 hou | 15 | 362 584 62.0 4689 8.0 33 13 | 55 215 2 |
| 1991 hou | 16 | 404 655 61.7 4690 7.2 23 21 | 33 68 2 |
| 1992 hou | 11 | 224 346 64.7 2521 7.3 18 12 | 27 147 1 |
| 1993 hou | 15 | 303 520 58.3 3485 6.7 21 21 | 48 145 1 |
| 1994 min | 15 | 371 601 61.7 4264 7.1 18 19 | 27 55 0 |
| 1995 min | 16 | 377 606 62.2 4228 7.0 33 14 | 33 82 0 |
| 1996 min | 8 | 134 247 54.3 1610 6.5 7 9 | 9 6 0 |
| 1997 sea | 15 | 313 528 59.3 3678 7.0 25 16 | 17 40 1 |
| 1998 sea | 10 | 145 258 56.2 1632 6.3 11 8 | 16 10 0 |
| 1999 kan | 1 | 1 3 33.3 20 6.7 0 0 | 0 0 0 |
| 2000 kan | 2 | 15 34 44.1 208 6.1 1 1 | 2 2 0
He played in the CFL because teams weren't trying to have a starting black QB in 78, not because he wasn't good enough to be in the league. I don't think it's fair to punish a player because of racism. Moon is one of the top passers and 6 yrs of his career don;t count (due to the CFL, where he was setting all kinds of records).
Moon played in a good passing system, but so did other great QB's (i.e. Montana in the West Coast offense). He never had a top notch receiver like Rice (closest he had was Carter when Moon was past his prime) and he never had a top notch RB (like Aikman, Farve, Manning or Elway). To have him off the list when his NFL numbers alone have him in the top 10 is a joke.
The only knock one has on Moon is that he didn't win. Using that criteria, a lot of the players on this list don't belong.