You're not a serious person are you? There are many first D pairs that are better than York and Sanheim, They're not a legitimate top defense pairing.
Let's look at a basic metric. Last season, at 5 on 5, Ekblad had a GF% of 68%, Forsling 66.99%, Larsson 55.06%, Montour 52.33%
This season, Sanheim 48.15% and York 47.92%. Admirable but not great. I know, you'll come back with goaltending
There is no obsession with magical players. There is a real world understanding using common sense that you need high level elite talent to win the Stanley Cup. The difference between the 20th best scorer and the top scorer is a chasm and is the difference between Travis Konecny and Nathan McKinnon
No, it's better to trade players and get a future assets than overpay to re-sign a player. Versus just overpaying with no future assets. Again, you're not understanding why some teams have more 30+ aged players versus others. Smart teams do not re-sign a player like Nick Seeler to a 4 year deals with trade protection.
GF is +/-. As anyone who knows metrics will tell you, it's meaningless b/c it's as much the goaltender and puck luck as anything else.
Last season, only 24 pairs played 800 (5x5) minutes together, only 19 played 12+ minutes a night.
Of that group of 12+ a night, York - Sanheim were 13th in xGF% at 49.66%
The top pairs by xGF%: Ekholm/Bouchard, Burns/Slavin, Gavrikov/Roy, Sanderson/Zub, Hronek/Hughes, Doughty/Anderson, Toews/Makar, Skjei/Pesce, Montour/Mikkola, Ceci/Nurse, DeMelo/Morrisey, Oleksiak/Borgen,
Sanheim/York, Trouba/Miller, Larsen/Dunn, Fox/Lindgren, Jones/Vlasic, Leddy/Parayko.
This season so far, 22 pairs have played 400 minutes and 12+ minutes a night.
Ekholm/Bouchard, Siegenthaler/Kovacevic, Ghost/Walker, Gavikov/Anderson, Orlov/Chatfield, Pesce/Hughes, Burns/Slavin, Dillon/Hamilton, Toews/Makar,
Sanheim/York, Ekblad/Forsling, Jensen/Chabot, Pietrangelo/Hanifin, Middleton/Faber, DeMelo/Morrisey, Werenski/Fabbro, McDonagh/Cernak, McNabb/Theodore, Anderson/Bahl, Oleksiak/Montour, Weegar/Miromanov, Ceci/Walman
Ghost/Walker are the 3rd pair on CAR and are sheltered.
xGF for top D-pairs is strongly influenced by the quality of forwards since they play with most lines fairly evenly distributed at ES. Either Montour suddenly became much worse or he's playing with forwards that aren't as good as last season.
What stands out is how teams "spread the wealth," often the top two pairs split the best two D-men, either because of preferred side (RH/LH) or because they want two solid pairs over one really good pair.