Like I said there is a reason why he is not worth what you are saying. Most teams will look at his historical defense, and it is bad, recognize that he is in maybe the easiest CF in baseball and is only average and deduce that if he goes to their team he will probably play bad defense because he won't be in one of the easiest CF in baseball to play for half his games. So his average defense hear for two seasons is not going to change most peoples belief that he would bad just about anywhere else.
His 250/350 away from Coors is good, but it makes him much like Shin-Soo Choo who is making 20 mil a season now and just about everyone thinks that contract is terrible now.
Right now 255/321 is the average for all MLB. So he is a player who tends to miss 15-20% of the season, plays below average to bad defense for most teams in CF and caries a 0.035 OBP higher than the MLB average. Being on the wrong side of 30 is not going to help him either. He is not worth 20 million and no team will give it to him. GMs look at more than WAR, and in his WAR was never over 2.3 until he came to the Cubs (FanGraghs WAR, I think that is the one you like).
For well over half the teams in the league he is a 2 WAR player (at best) because his defense goes back to garbage and he still is an average hitter with above average OBP who misses ~30 games.
I understand your argument. I just disagree. With regard to his defense, Colorado had him play shallow when he was coming up and it has hurt his metrics. That's one change the cubs made this year and why he's looked a lot better. I could link some articles that talk about it but basically the gist of it was balls hit over your head have a disproportionally bad outcome to balls hit in front of you. Fowler is by no means a slow guy but by playing so shallow more balls went over his head.
As for him being Choo, Choo would be a fine contract... if he actually could play CF. He couldn't play CF when he was young before that contract. His big year with the Reds he was -17.0 UZR/150 and -18 in DRS. The year prior to that in RF for the Indians he was -10 DRS and -15.8 UZR/150. Fowler hasn't really been that bad. He had 3 particularly bad years that were almost entirely based on his range. Some of that had to do with the previously mentioned shallow play and I'm guessing some also had to do with the numerous injuries he suffered. Either way, he had several years in Colorado which is a huge OF where he was just below average. He's not Willie Mays back there but he can play the position. Choo should have never been in CF.
Honestly, the only real argument I see against him at this point is the injury one. But frankly that's an argument you can make against anyone who's a FA. That's why I see him getting 3-4 years rather than 6-7 a la Ellsbury.
At the end of the day, he's been worth 6.5 fWAR the past 2 years with the cubs despite having a horrible start to 2015 and missing a month this year. So, barring another injury this year, that's probably 7 fWAR by the end of the year and maybe more. At 3.5 fWAR per season that makes him one of the 50 most valuable position players in baseball. Upton who was worth a similar 3.6 fWAR last year got 6 yrs/$132.75 mil. He's a little younger and has a bit more power but that's $22.125 mil per season. I mentioned Gordon's deal at $18 mil/season with similar production. That's roughly where I see his value. Whether or not teams pay him that is obviously another issue but I'm betting the O's wish they could have a do over on the deal they failed to sign him to. That was supposedly 3 year $35 mil in a super rich FA market. This coming year is fairly barren. If he doesn't get $18 mil/year I'd be surprised and if he's lower than that the cubs had better be in on him in that $15 mil range.
