So, there are actually some very good reasons to believe that someone else will be better than CJ next year.
1) He just had his career year, and it's not going to happen again.
That's kind of a risky statement. I don't really feel that's a fact at all. I agree with you that getting 360 carries is unlikely, but that doesn't mean he's had his career year. I don't think its unrealistic he could put up another 20-25 catches and not lose many total yards from what he did this year getting about 300 carries, plus its possible and perhaps likely that he'll put up even more TD's in the coming years. A 2,200 total yard(let's say 1,600 rushing and 600 receiving) and 20 TD season would be a better fantasy season than what he had this year.
It's not a risky statement at all. It's much more of a risky statement to say that this wasn't Johnson's career year, and he will improve on it (either in NFL terms, or FF terms).1) It is much more likely that Johnson will never break his yards from scrimmage record again than that he will break that record again.
2) It is much more likely that Johnson will never rush for 2000 yards again than that he will break 2000 rushing again. (No NFL RB has ever rushed for more than 2000 yards more than once)
3) It is possible that Johnson will not rush for even 1600 yards in a season again. (23 NFL RBs have managed to rush for over 1600 yards in 1 season, only 10 of them were able to duplicate that feat; to be fair, though, 4 of the other 5 RBs who rushed for over 2000, rushed for 1600 at least one other time in their career).
4) It is very unlikely to assume that Johnson will break 20 TDs. It's a rare feat (RBs have accrued 20+ TDs only 22 times in the NFL). Johnson isn't the typical RB who you would expect to score 20 TDs. Most RBs who hit that mark not only have homerun potential, but also get a lot of short yardage TDs. Johnson scored 7 TDs from over 50 yards in 2009, but he only scored 5 TDs from inside of 5 yards. It's more likely for the long TD #s to come down than for the short TD #s to go up. That makes getting 20 TDs very difficult.
I'm not saying Johnson isn't a top 5 (or even top 3) FF RB, but Peterson should be the #1 ranked back for next year. He easily has the potential to get over 1500 rush yards, plus several hundred more through the air (as we saw in 09, he can be more of an asset in the passing game). He gets his team's short yardage carries, and he has homerun ability, as well (7 TDs of over 50 yards in his 3 year career), he doesn't really have a back to take carries away (Taylor took some ADP's rookie year, but the last 2 years, Peterson has been the lead RB).
If you disagree, explain why Peterson shouldn't be the top back, even in a PPR (where Johnson had only 7 more catches in 09).