A bad Letang is still very good comparably. Anyone who thinks Letang's contract would be hard to move has no clue what they're talking about. You got wingers making as much as Letang. And believe me...Letang is way way way more valuable than Evander Kane or JVR.
Hell, Shattenkirk is making the same basically, he is not near Letang. (Letangs contract is very good)
I laugh at people wanting to move Letang but WANT a guy like Justin Faulk who is dreadful defensively and hasn't put up great offensive numbers in a while. While facing much weaker comp than Letang. Faulk would be eaten alive as a #1D. Letang atleast has proved to be able to hold his own, even play at a Norris level as the #1 D.
[edit - this turned into a much longer post then I'd planned on writing]
There's multiple issues when it comes to Letang.
A) His cap hit. No, 7.25m isn't expensive for a #1D. However his play for much of last season and intermittently in the POs wasn't #1D caliber. And I'm not even talking about the big blunders that lead to brutal goals, but just in general. That said, if he plays at his historical average, he's a #1D. But that leads to issue 2.
B) His health. If you can't trust him to stay healthy, then it doesn't really matter how good his cap hit is. Prior to 14/15 some (much?) of this board's attitude was "well he's healthy for the POs". Then he missed 14/15 and 16/17. I'd happily pay more for a better D, and I'd happily pay less for a lesser D... if I knew that they were going to play at a fairly consistent level for 75+ games a season.
C) His age. Most of the players we're talking about are younger then Letang. Shattenkirk is 1.5 yrs younger. Faulk is 5 years younger. Nisky is the same age. But looking just at Letang, there's some serious (and legitimate) questions as to how he will age due to the fact that he's not exactly the smartest player out there. Letang gets by on his skill and skating. If his hands and/or feet go... it will get really ugly out there. People bitched about Hainsey in 16/17. But if Letang had Hainsey's IQ, he'd be untouchable, and we the fans wouldn't even consider moving him. That IQ is what really extends players careers, and it's something that Letang far too often is missing.
D) His consistency. Not even season to season or game to game.... Letang from shift to shift can go from looking like Lidstrom or Karlsson to looking like Pouliot. Hell sometimes you see that on the same shift. Prior to his neck injury it had looked like he had sorted out most of that, and I'll give him the benefit of the doubt that he can figure it out for next season... but it's not like it wasn't something that we've discussed about him prior to last year.
You brought up two names (and I added a 3rd). And while none are as good as Letang (even if you average out the past 3-5 seasons prior to last yr), or have produced as much as him (while also usually not playing on as good/offensive teams like him), they've produced enough at a lower cap hit that I'd seriously consider swapping them 1-1. It might be a loss in dynamic talent... but younger, cheaper, and healthier... has a value all of it's own.
Shattenkirk missed 40 games over his 6 seasons with STL. Rough season with NY last season, but even so, he's 600k cheaper then Letang. Faulk in the past 6 seasons missed 47 games. He hasn't had anything close to Letang's production, but then his team has also historically been very bad (4x top 7 picks,+ 2 more top 13 picks, and picked #2 this summer, and over the last 7 seasons averaged 25th in GF). He's also 5 years younger and has a cap hit that's 2.42m cheaper (although his next deal in a few years will nullify most of that). Niskanen isn't any younger then Letang, and he's certainly not better then him. But he's 1.5m cheaper, and in the past 7 seasons only missed 34 games.
In that same span, Letang missed 154 games.
I mean sure ideally you get Karlsson to replace Letang, and then everyone is happy. But we don't actually need that. If we get down to the bare necessities, we need a RHD who can skate well, handle the puck decently and who can make a good first pass. And they need to be good enough defensively that you can put them out on the ice for 20-22 minutes against quality players and not hold your breath the entire time. PP/PK would obviously be a plus, but with the other blueliners we currently have, that's more of a plus then a need.
I've been vocal for years (prior to 16/17) that you do not need a #1D to win a cup. That said, it's hard as f*** to assemble and then retain for multiple seasons a blueline that has all the needed parts (PK, PP, transition/puck movement, ability to eat the required minutes) without having a #1D fill multiple roles there. Depending on how much faith you put in JJ, I think we're at the point that this blueline would be awfully close to being able to have a "by committee" blueline. You swap out Letang for any one of those players (Faulk, Shattenkirk, Niskanen), and I think you'd still end up with a group that is capable enough to win. It would also be cheaper and/or younger, and looking at historical numbers, significantly healthier.
Bottom line is there's a lot more that goes into whether player A is better than player B then just their cap and individual skill. And the knowledge that a player will probably be available for the POs has a value all of it's own.