Hindsight is always 20/20, but I thought the Leddy trade was unnecessary from the moment it was announced. It was a move for the sake of making a move, that didn't make us appreciably better short-term and had the chance to make us worse longer-term if (when) Leddy was brought back. It pushed the team further into "win now" mode at the expense of someone who could fill an NHL roster spot with a chance to grow some, and bound our hands with respect to the cap at a time we already knew the cap situation was tight and we could use a little flexibility. [Losing Sundqvist, who's finally over the ACL injury and looking at least competent with the Red Wings and would have provided stability here, is just salt in the wound.]
Walman was someone I said for a while had max upside as the weaker half of a 2nd pairing. The question was whether he would ever unlock it. We can all question whether he'd have done it here, but certainly the Walman we saw showed flashes of potential, even if he would have stretches where he'd play tentatively and look poor defensively as a result. You know, like with Dunn: had potential, questions over whether he'd hit it, was showing signs he wouldn't. Except with Dunn, he'd make mistakes and get burned and go right back out and do the same thing like he hadn't learned anything and didn't care about learning anything. [Which is why we left him out in the expansion draft; if he "got it" elsewhere, awesome for him and them - but he wasn't doing it here, and increasingly acted like he really didn't care.]
Would Walman have benefitted from more playing time, more games to gain experience, gain confidence, play through his mistakes and learn? Possibly. At the time of the trade, Walman had 58 NHL games under his belt (57 regular season, 1 playoff); Niko Mikkola had 85. If you were banking on Mikkola's potential - I think he's nothing more than the weak half of a 5/6 with limited additional upside, who other teams will overpay for thinking there's more there - then there's a great argument to have done the same thing with Walman.