I think Fletcher wanted Hartman because he is a talented player, and has more upside than any late 3rd rd pick.
They got a chance to see Hartman for half a season, and realized there's a reason he was available.
Then traded him for a useful depth piece to buy time for their LHV prospects.
It was a reasonable gamble, sometimes a change of scenery can revive a player's career.
Pitlick is a valuable piece for a team with playoff aspirations, he's low cost, doesn't block anyone and can help solidify the 4th line and PK if he can stay healthy.
Quibbling about deals like these is silly, late 3rd rd picks have limited value, they're often used to add players like Pitlick.
At some point, incremental improvements to the NHL team are more important than incremental improvements to the talent pipeline - especially when you already have so many similar prospects in the pipeline.