My problem with Heyward - and for the record I agree someone is going to pay him that much - is that he's a BIG guy, defense/baserunning peaks early, and his offense never came around. Interestingly, offensively he's a bit like Ryan Zimmerman. Heyward's two big early years averaged about 27 offensive runs produced and Zimmerman's were 29. Bu neither was able to sustain really high offensive production for whatever reason and became just okay hitters.
So my worry for Heyward is the same as for Zimmerman, in retrospect: what happens if injuries/age sap his defensive/baserunning value? Then you're taking a big bet on Heyward's bat, or else he's a $20 million/year 2 WAR player. I just find it hard to believe he's going to be producing 1.5-2 wins of value out of his legs and in the field as a 6'5" 250 lb RF into his 30s.
That's going to be a concern for every OFer who has good base running and defense. But Heyward is 26. Age should not be an issue. Injury wise ... I can see the concern. He's the same height as Werth, about the same size. He has had some injury concerns. But in terms of regression, Heyward shouldn't have any. In theory, he isn't even in his prime yet. And you run this age/injury regression issue with every free agent.
But Heyward is posting his best batting average and OBP since his rookie season. Heyward is swinging at the same number of pitches, but making contact and still not striking out a lot (~16%). That's huge on this team. He's shown what happens if he gets healthy. And if you discount the horrendous start the first month of the season, in which he had some bad luck and was also adapting to his new hitting approach/stance, he's put up some great numbers. An OPS well over .800. GG caliber defense in RF.
Combine that with a nice pay day and a chance to face his old team again, and yea, the Nats could grab themselves a nice outfield.
I kind of agree (a reason why I don't think he'll stick in CF either). Depending on the price, Cespedes, Upton, or Gordon look better options.
Gordon will be over 30 and, so far, can only play LF. Cespedes will be 30 and he has the kind of skill set that will regress fast. You dislike strikeouts now? Just wait until his climb up about 10 points.
Justin Upton would be unique, but you have another high strikeout guy who plays really poor defense in LF, but a decent arm.
All three of those guys are guys you sign and say, well, I know he got 5/6/7 years, but I'm really expecting about three years worth of production out of them. Heyward is someone you sign for 8 and say I'm getting 3-5 years of prime production.
Heyward is a guy you sign to continue to compete right up until Harper's contract runs out and in to his extension. That's a monster part of the lineup, with guys like Turner and Difo (hopefully) progressing in to top of the order hitters.
