These questions aren't simple to answer.
In baseball, we have very developed cumulative statistics that allow us to compare value. We are able to identify exactly how much of a player's performance contributes to his team's success. The unit of measurement is called WAR, or Wins Above Replacement. The more players a team has that contribute positive WAR, the more wins the team has during the season -- easy. So, when a rebuilding team trades its star 1st baseman for multiple prospects, we compare the "Wins" accumulated by the MLB player over the coming years to what the prospects eventually yield (1st Baseman earns 12 WAR over the next three seasons, while the two prospects combine for 11 WAR over a similar time span -- therefore one might argue the team that traded for the 1st Baseman narrowly "wins" the swap).
Hockey is just now getting around to quantifying performance in this fashion. War-On-Ice.com has set itself apart as a innovator in this field, attempting to take the statistics we know directly correlate to winning and merge them to create a similar Wins Above Replacement statistic. Often, it yields a number we can already discern with our own eyeballs (ie. Gabriel Landeskog with 8.46 wins last year vs. Brad Stuart with -8.11 wins), and sometimes it's revealing in a way we wouldn't have suspected.
The last major trade the Avalanche were involved in sent enigmatic Chris Stewart, top-prospect Kevin Shattenkirk, and a 2nd Round pick to the St. Louis Blues for former No. 1 overall selection, Erik Johnson, useful 3rd-line center Jay McClement, and the upcoming No. 11 overall pick. That was in 2011 and we still don't have enough information to make a definitive statement. Johnson and Shattenkirk have developed into All-Star defensemen, Chris Stewart has been almost a total washout, McClement had his best season his next year for Colorado (but was shipped off again a year later), and Duncan Seimens (the No. 11 pick) has yet to make the Avalanche as a full-time player. So far, it's difficult to make a proper evaluation.
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Ryan O'Reilly earned 8.29 wins last season according to War-On-Ice, which is pretty close to his career average if you throw out outliers like his -3.72 win rookie season and his otherworldly 17.13 from 2013-14 playing on Matt Duchene's line. Jamie McGinn, if you throw out his best and worst season has averaged 0.64 wins per season over his career. So, according to the statistic, the Avalanche need to replace an average of 9.01 wins going forward. Is it possible through the players received in the trade? What if we add the other players added through free agency with the money saved? Let's find out:
It's been widely speculated that the Avalanche are worse off for next year with what's transpired this offseason, that Buffalo is better in the short term. However, using this Wins-Above-Replacement metric, that likely isn't the case. Carl Soderberg, over his short North American career has averaged 5.83 wins per season (throwing out his rookie year), Francois Beauchemin has averaged 2.9 wins over his long career with Anaheim, and Blake Comeau has average 1.94 wins over his career (including 6.39 last year). Add it all up, and the new Avalanche acquisitions average 10.64 wins per season. Maybe O'Reilly is closer in ability to his 2013-14 outlier, and maybe the Avalanche players all regress into hot garbage, but the statistics suggest Colorado is probably better next year with these new players alone.
But we also have to consider the young prospects received from Buffalo, who will almost certainly be playing in the NHL next year. Right now, we don't have enough of a sample size to make very accurate projections. Nikita Zadorov in 60 games as a 20-year old on the worst defensive team in the league was good for -7.27 wins last year. Perhaps this is representative of his true ability, but many in the game consider Zadorov to be a top defensive prospect in the game and a future top-pairing defenseman. It's very likely, with sheltered minutes, he develops into at least a replacement-level player in his second season. But perhaps most interesting is Mikhail Grigorenko, a player considered by some already to be a draft bust already at 21-years old, but in just 25 NHL games last year, the young Russian was good for 2.61 wins, which is impressive and suggests top-line ability. Extrapolated over 82 games, this WAR metric suggests Grigorenko is as valuable as Landeskog.
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Again, we can't know who's getting the better end of the deal right now, but it's very possible Colorado is going to come out ahead this offseason, despite the prevailing media narrative that suggests otherwise. Can O'Reilly be better without playing with players like Landeskog and MacKinnon? Can Zadorov develop into an effective defenseman? These are the questions we're going to start finding the answers to next season. But right now, I think "Avalanche are worse" stories can go away.