Warning: Advanced Skepticism
Look at Tierney's first chart called called 'Offense'. The X axis is labeled Quality, the Y axis is results. For me, this ought to produce, more or less, a straight line from bottom left to top right, because there ought to be a relationship between the quality of your chances and your results. Since xGf/60 doesn't relate to your results, it means that it's not the xGf/60 that is creating the results, it's something else, which I'll come back to.
Now let's look at the second chart called 'Defense'. It produces, more or less, a straight line. Demonstrating that xGf does relate to your results in the defensive zone. I'll save the discussion of how the first chart relates to the second chart for another day.
I believe that 'something else' is what happens right before the distance and type of shot are taken. If the puck moves horizontal through the zone, it creates a higher scoring chance than if a player takes the shot himself. If you've been listening to my podcast, I've been talking about how poorly the Sabres move the puck through the offensive zone. In Buffalo, it's mostly Eichel that moves the puck horizontal. I grade Vegas highlights as a comparison, where the entire team moves the puck horizontal (Though no one passes the puck to Carrier, like no one in Buffalo passes the puck to Girgenssons). I believe this horizontal puck movement creates higher quality scoring chances.
NHL.com forces me to listen to the opposing announcers half the time, and that's been interesting as how the different announcers talk about their team (and how they talk about the Sabres, but that's another discussion). The St Louis Blues are very good at moving the puck horizontal in the offensive zone. The announcers talked about this during the last Sabre St Louis game, talking about how the coach of St Louis preaches being patient in the offensive zone. That the Blues' players are taught not to take the low percentage shot, but to wait for the high percentage shot. For me, the Blues dominated both Sabre games, that Ullmark stole one because the St Louis back up goaltender was bad in the first meeting. Similarly, (it was a while ago now, so my details will be off) I think it was the Washington announcers were talking about how the Cap's coach preaches getting high percentage shots. Contrasting that is Buffalo, where Rob Ray, every game, talks about the need to 'Put pucks to the net', or as I translate to 'Take low quality shots'. I believe this belief system is rampant in the Buffalo organization.
Kreuger gives me hope despite my lack of confidence. Reinhart is moving the puck more in the offensive zone than he had been. The power play goal of Risto passing to Reinhart last night (while not horizontal, gave Reinhart and open look) gives me hope that the Sabres are working on getting higher percentage shots.