The thing is you can't possibly watch EVERY game for EVERY player on EVERY team, that goes for full time scouts, gm's, coaches and is even truer for fans who want to form an idea on a player they don't get to watch often.
I think that numbers on a spreadsheet can be a good way to capture a snapshot of a player over all games. You can go watch a player once or twice and be amazed, but then if he doesn't do anything the rest of the year how are you gonna know? If someone watched Gagner's 8 points game and never anything else, they might have given a lot to get him no? Ditto for Hertl and Eller.
Also, when talking about numbers, it's the sheer volume of them that makes them more powerful, and that's why it's very difficult to find meaningful measures in hockey, since you only get so many data points to look at. That's why it's easier to come up with measures for goalies too, they're on the ice for all shot against and all goals against. There is a lack of data points. In your example of zone entries, you could glean context from speed of entry, time of possession after entry, did the entry lead to a goal? Etc. Etc. Yes you do have to record all that when it happens, like any other data out there, but then you can put it all together in one place to get a snapshot of a player.
Now, I'm not saying analytics is the end-all be-all, it's extremely difficult to predict the result of a game on any given night, nevermind the Stanley Cup winner. But, really, who saw Dallas making the finals, analytics vs old-fashioned opinions? Who watched the games and said "Ahhh, I think Dallas is going far this year. In fact, it might be their year!". I don't think anyone predicted that lol
Edit: In fact, I just did a re-read of some predictions for the play-ins and 1st round, and most "experts" saw Dallas out IN THE FIRST ROUND.