I think are both ideally suited to a third line role on a team that isn't the Jets. Or isn't coached by Maurice. I'm not knocking Lowry in the sense that his line tilts the ice in the Jets favor, but they score so little. But a balanced minute spread between a third 'scoring' line with Harkins/Ves/X and a killer fourth checking line of Lowry/Copp/X with the minutes being pulled back from the 1st line still seems worth investigating to me. Or reverse the line designations if it makes you happier.
Of the two, I think both get undersold to be honest. Few will remember that Harkins in his draft year was at one point mentioned as a first rounder (in the September before the draft occurred) - I was thrilled to get him where we did. Obviously he fell considerably from that but at one point he looked pretty good. I think he's worked his way into a strong position and will have a solid career in the NHL, though I'm not sure he'll ever get much more than a two year deal from anyone. Not that it matters, I'd be ecstatic to be signing 2x $1.1 deals for my entire career once I realize I'm not getting first line money. I could play ten years and make more than most people ever will in their lives.
Ves on the other hand gets undersold as well. Nobody seems to recall he was drafted 24th OA rather than 10th or 13th or something like that. He's never had the notional suggestion of being a center, an advantage that Roslovic has had and probably afforded him a different trajectory (with similar outcome?). He's also European and has had to adapt to the American game and ice surface, something Jack grew up in (yes, I know we're talking about Harkins, but Roslovic has similar draft position being a first rounder). So he didn't knock down the barn door. Oops. Wheeler-Connor, Ehlers-Laine, Copp - X (Lowry). Where was he supposed to fit in there? The Jets had exactly zero need to rush him through his development and have taken their time with him. He seems to have realized, based on his own recent comments, that his early expectations were unreasonable.
Harkins will be a good utility guy for a long time. Ves has the higher ceiling still.
If you want to talk who is being undersold more, I'll go with Vesalainen. This is the same board that had a substantial number of posters that were ready to give up on a kid named Morrissey after he "couldn't get out of the A" for two years.