Wayne Primeau
Stay Gold
Deryk Engelland is pressbox fodder on most teams except the Flames, who have no defensive depth or size whatsoever and are unwilling to play prospects. In fact that's why Engelland was picked up at such an absurd price anyways, a payment he himself was surprised by.
As for Diaz, he's been the better player of the two for a long time, carrying that pairing in pretty much every metric. But as a smaller player on an already small team, he had an upwards battle to climb to establish himself as a regular.
...Smid's been terrible, since he's been paired with Engelland instead of a puck-mover like Russell or Diaz. And looking back historically, Smid's been an okay bottom pairing defenseman while Engelland has played mostly goon-forward.
Nikitin would be an upgrade over either Smid or Engelland.
Just to point out -
Considering that the Flames' top 4 is in the top five, if not the top three, in the NHL, I find it unwise of you to claim that they have no defensive depth or size whatsoever.
Also, are you just calling the Flames small because of Gaudreau, Byron and Russell? One of those guys is a depth guy, and the other two are two of the Flames' best players. I can go on and on about this topic, but I'll just say this - those three, along with Jiri Hudler, are the only players on the entire team smaller than 5'11".
Unless you are looking back at Smid's history with the Flames where he's been shadowed by the aforementioned elite top 4, he has actually been a top 2/4 d-man for most of his career, that being with Edmonton.
Nikita Nikitin is in no ways an upgrade over Deryk Engelland, who has actually been playing some fine hockey lately. Smid's been hurt for most of the year and when he's been playing, he's been doing so with an injury, so there isn't much leverage to that part of your argument.
Just thoughts.