Hey Vinny,
I haven't been watching games much this year (I tune into a 3rd period now and again), but the whole idea was that MavLam and Sima were going to be the twin towers back there. If he's doing well in Tucson (and I believe you if you say so), then no way you trade him.
If Kesselring has passed Durzi on the depth chart that's insane. I believe you, but it's still insane. Quick look at fancy stats show that Ian Cole and Kesselring have been good together -- there are so many dangers about just relying on stats without really watching the games (which I hate, but it's what I'm doing right now), but at a top level according to the fancy stats Cole and Kesselring have been a well-above average 5v5 pairing (haven't properly indexed for matchups / deployment, that would take too long).
If all of that is true... I think Durzi is the guy to trade because he's got the best name recognition. Durzi's signed thru 2028 at 6m (no idea whether that's a good contract), but prior to this year I thought he was a good 2nd pair so that number seems fair. And teams do like cost certainty so the contract length may help.
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Would Durzi and a 2nd get a good young 2C player / prospect? Probably. What about Durzi and Maccelli (I like Maccelli a lot, but doesn't seem like there's enough room for him in our top 6)? I think probably that's a pretty good package.
I do agree that roster construction-wise this roster does need a 2C unless you think Hayton or McBain will get there -- Hayton's not terrible in that spot but I think if you actually get a legitimate pass first center for Guenther, maybe Guenther gets to 40-50 goals and then the team has legit secondary scoring and is obviously more dangerous. With where we're picking, you should be able to draft for a 2C though, and BA has a strong history there. So I don't know if a trade is strictly necessary -- not the worst idea to hold onto defensive depth -- also Ian Cole is 36 and only signed through 2026, if MavLam / Sima cook down in Tucson for an extra year that's not the worst thing ever. Also gives Hrabal a bit more time to cook as well in net.
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Anyway those my thoughts from out here without following the team all that closely. IF the D are good enough, then does Durzi + Maccelli for a young, pass first 2C make the roster better? Yeah, it probably does. But trading away D depth (which would sort of force Sima into the NHL relatively quickly) has its downsides too.
All that to say I think both options (trading or not trading one of the extra D) are good options. That's a lot of words for a non-answer! Ha
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EDIT: Imo there should also be a poll option "Keep all 3" that's what I think I would lean toward