I agree with a lot of what you're seeing. I'll extrapolate on some of your points.
Quite often I see people saying:"baseball and basketball are easy to analyze. They're discrete games in a way compared to hockey". I'd argue that even though, yes some parts of baseball are easy to analyze ... btw, we have such easy objective data in hockey like goals, assists, who's on the ice and whatnot ... Baseball analysts still had to go much deeper in the data.
As great as moneyball is as a book, the A's were still only an average offense. Although it is true that they were able to generate average offense with one of the smallest budget in the league and that provided some good value for the team. Their bread and butter was on defense. The moneyball narrative would be much less interesting if it went "How a budget team was able to become average."
Same for the Tampa Bay Rays. Once their GM, fresh of wall street, came in. What made the Rays and A's a contending teams was BABIP. Batting average on balls in play. Rays introduced all those quirky defenses we see in the league nowadays. Even when traditional baseball analysts thought you couldn't control where balls fell into play these guys went further than the crowd and developed their own metrics. They had to do this through basic scientific research and get their own data by either watching games or using softwares.
The same holds true in hockey. Although there's already quite a bit of an advantage to gain from various "advanced stats"... as seen with guys like MacArthur, Jagr, Grabovski, Weaver and so on ... The bread and butter of an analytics team will be to develop their own metrics by analyzing video data. Other sports aren't that much easier to analyze in the end.
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Sports leagues aren't open markets. So, it's quite hard to have any kind of evolution when league members decide on who their competition is.
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You're right, outside of the Tampa Bay Rays, very few teams have more than 2 or 3 people working in their analytics department. That said, there's quite a few businesses that have developed over the years and consult with teams on a regular basis.
Something being easier doesn't mean it's easy. No one, at least that I've seen, doubts that a ton of work and intelligence has gone into and still goes into baseball analytics. It's clear that many very intelligent and determined people spent a great deal of time developing some of the advanced baseball statistics.
However that doesn't change the fact that hockey is a much more dynamic game than Baseball.
In Baseball there are roughly 200 discrete events per game (pitches) and even the majority of those don't have anything happening in them aside from a single event (a pitch). Since they are discrete events and don't really flow into each other it's much more feasible to pull similar situations from other games and get a wealth of data.
In Basketball you have a majority of the game happening in a set half court offense. The point guard brings the ball up the court at a modest pace and everyone sets up and runs some set plays. Yes, there's fast breaks and transition games but those still have very defined roles for the teams.
In both sports one team is very clearly on offense and one team is very clearly on defense. Baseball is obviously the most set like this. There is no connection between how your offense performs and how your defense performs aside from momentum or potential pressure (if your pitcher is getting lit up you might be more inclined to swing for the fences or take a risk to score a run). Basketball is a little more linked because of transition and fast breaks but there's still a lot of set team A on offense team B on defense type plays. Yes, being better defensively helps you offensively in that it gives you slightly more possession time, but you cannot dominate a game offensively by being amazing defensively and vice versa.
In hockey those relationship are a lot more grey. Take the Team Canada in the Olympics. They had one of the best defensive performances of all time in the Olympics. Yes, that's partly because of good defensive systems and skill but it was also because they were dominant offensively. One of the biggest reason they were so stifling defensively is because they just didn't let the other team have the puck. Theoretically a perfect defensive game is one in which the other team *never* touches the puck and thus you're never actually playing defense. Changing your offensive system naturally changes your defensive system and vice versa.
Plays are naturally a blend of offense and defense. A defenseman pinching in is an offensive play, but comes at a defensive cost. A forward coming back early to help out the defense is a defensive play, but comes at an offensive cost.
In Baseball you can have weird defenses like having 3 infielders on the left side of the infield, your center fielder in shallow right field, your left fielder in mid left-center and your right fielder back near the home run pole. Absolutely none of those changes has any effect on your team when it's your turn to bat.
In Basketball you can overload a defensive side, or double team someone, or play a tight zone or a loose zone and although there's some offensive impact in how you can transition, for the most part you can run both your defensive and offensive games separately. In hockey you really can't. Having Couturier shadow Crosby in the defensive zone naturally affects where he'll be when you're moving into the offensive zone.
That doesn't mean Baseball is easy or that hockey is impossible, it just means that any analysis is naturally less cut and dried.