Wrong. His advanced stats took a nosedive. Either way, he was a shitty defenseman throughout. JapersRink did a whole write up on this year's ago. As a former season ticket holder who watched every one of his games, he was never good and struggled to be adequate, even when the advanced stats said something different.
I think I understand where you've misinterpreted those stats. Schultz's GF% looks really good in 2010 because (as I'm sure you remember) the Caps won the President's Trophy. Almost everyone on the team had a really good GF% - because that's what happens on a team with 120+ points. Look at last year's Bruins, almost every regular is at 57%+. They don't have 18 superstars.
It's usually more instructive to look at how a player looks relative to their teammates. (Raw GF% mostly tells you about the quality of a player's team, not his individual performance. As an example - Karlsson jumped 10% between 2018 and 2019. Did he suddenly learn to play defense, or was he traded from a bad team to a good team?). Relating this back to Jeff Schultz - most "advanced" metrics (CF%, FF%, and xGF%) show that he was pretty much average in 2010.
As for raw (or even relative) GF% - Schultz's on ice save percentage was 94.6% (at 5v5). That means he either found a way to turn an aging Jose Theodore and two rookies into a goalie who was significantly better than peak Dominik Hasek. Or it was a fluke. (That explains his +50 rating). It was obvious this was unsustainable. Predictably, when he played in front of still good (but not extraordinary) goaltending over the rest of his career - he looked completely unremarkable.
I think Schultz is actually a good example of how "advanced" stats can give insights. Many fans were blinded by his +50. (So were professional hockey writers – he even got a few votes for the year-end all-star team, and one vote for the Norris trophy). The advanced stats made it pretty clear that his 2010 season was a fluke, and that he wasn't anything special. That seems to be the same conclusion that you, as a season ticketholder, came to.
But to your point - there are a lot of stats out there. It's often unclear which ones are relevant, and/or which are sustainable. I think Jeff Schultz is a bad example because the numbers pretty clearly show that he was an unremarkable defensemen (even when he went +50 and got votes for the all-star team). I think a lot of people dislike "advanced" stats because it's hard to figure out which numbers to look at, and it can be overwhelming to separate what's useful from the noise.