Bennett's draft position is not completely irrelevant because he still has alot of potential and often shows that potential. Bennett still has considerable value to the Flames, which is what matters most in this scenario. Bringing up Gaudreau just shows you are desperately grasping for straws, not at all shocking considering you fail to grasp that different times of year net different types of returns.
Stone will get a decent return, yes, but not one as valuable as you listed, a GM paying that would have to be an absolute ****ing moron. Bennett will very likely still become a top 6 forward, that first round pick has alot of value, Dube has outplayed his draft position and has good value. Basically you're suggesting a value (to the Flames) of essentially 3 first round picks. Which Stone is absolutely not worth IMO.
If Bennett has as much value as you assume, the Flames wouldn't have gone out of their way to acquire Neal, Lindholm, Czarnik, and Ryan. They would have given him every chance to play a top-6 if not a top-9 role. He's way down the depth chart now. He's 22 years old, and he's coming off consecutive 26-point seasons (52 total points in 163 games). I understand wanting and hoping he will break out, but right now I don't see the team valuing him that much. All their moves to date point to the opposite.
And no, I'm not grasping for straws with the Gaudreau example. You just fail to understand the point, which to repeat is intended to demonstrate that draft position is meaningless. After four seasons, production and ability matter. If draft position meant something, Nail Yakupov would still be in the NHL. So again, Bennett's value, right now, is not that of a 1st-round pick. No team would trade a first-round pick for him. It's just like Curtis Lazar - a former first-round pick with little to no value (well Bennett has more value but he's not worth a top selection because he hasn't earned it). If anyone is grasping for straws to rationalize Bennett's value, it's you.
BTW, I do agree that teams will overpay at the deadline for certain players, such as a #4 defenceman or a checking third-line centre. But that's not the point I'm making. And to say one more time, when a premiere talent becomes available, regardless of the time of year, teams pay up because they are difficult to acquire. In addition, because he's available now and where a team can get him for an entire season as oppose to 25 games or less, that player's value increases. It's why Ottawa is trying to deal Karlsson now – his value is higher now than it will be come February 1st (or whenever the 2019 trade deadline is), not to mention more teams can get in on the action (deadline sees fewer teams involved due to cap restrictions and their playoff positioning).
This applies to Stone. And when player of his calibre - a surefire first-line winger and a right-handed shot to boot and can play in all situations - becomes available, the return will be big. He finished 14th in PPG last year (got injured to cut his season short), ahead of Gaudreau, Ovechkin, and Kuznetsov and just behind Crosby.
Think of it this way, what do you think is Gaudreau's trade value? That is essentially Stone's value, yet Stone kills penalties and plays a position where there is less quality and quantity.
Finally, why do you value Stone so lightly? Have you watched him play? He has great possession numbers and he's one of the league's best takeaway artists. I didn't think much of him when he first came up (thought Ottawa fans overrated him as a prospect), but he changed my mind quickly. He's not the fastest guy on the ice, but he's extremely intelligent, has a hockey IQ that is off the charts, and is highly skilled. He's like Blake Wheeler but better defensively and more of a scorer. Stone playing with Gaudreau and Monahan or Tkachuk and Backlund would be dynamite (Lindholm would play one of the top-2 lines). Then a third line of Frolik, Ryan, and Neil would be really formidable.
If Trevling could acquire Stone and get him to sign a long-term deal, he shouldn't hesitate to deal Bennett, one of the defensive prospects, Brouwer, and a first-round pick (can make it lottery protected in 2019). I agree the team should try to keep Dubé, but he wouldn't make or break the deal for me. If the Sens wanted him, then the quality of the defensive prospect would be lowered (i.e., no Valimaki nor Anderssen, but Kylington would be open game). Stone is that good.
Edit: I should have stated before that any deal with Ottawa would be contingent on Stone signing long-term. This wasn't clear in any of the aforementioned posts.