Hartline can be a good enough #2 WR on a team with a good quarterback. The kid can get open, he runs pretty good routes, and he actually can get open down the field with relative effectiveness. The problem with him as a #1 is that you really never see him do anything remotely spectacular. As has been discussed, he doesn't get YAC, he doesn't go up and get the ball over defenders on high throws, he's never going to draw double teams, and his lack of touchdown production is really glaring. 3 years in the league and 2 years as a starter for 5 TDs? Yeesh.
Could Hartline be a lot better with a better QB? Of course. You can say that about literally every receiver in the league unless his QB is Tom Brady or Aaron Rodgers. Problem is, he won't see better QB play this year... So moot point.
I really don't see the Jordy Nelson comparison either. While they are similar in height (Hartline 6-2, Nelson 6-3) Nelson plays at around 220 while Hartline plays at around 200. Nelson has way more muscle, he breaks tackles and he's a lot more explosive than Hartline. Production also has to mean something to you guys. I understand that Nelson has Aaron Rodgers, but in his first full season as a starter last year (while still in a loaded WR corps so he didn't play constantly) he had an absolutely freakish year and scored 15 times. Extremely impressive in any offense.
Like I said, Hartline can very well be a good enough #2 guy, but do you really have confidence in the guy to go out and beat the Revis', Nnamdi's and Joseph's of the world? Ugh. I sure as **** don't.