It's not just that the Sens were quicker, generate more pressure, play up-tempo all the time (instead of sporadically), and have 4 lines of energetic, well-conditioned players (while seemingly half our forwards look lethargic and poorly conditioned) - it's the difference between the 2 teams in transitioning from O to D and from D to O. The Sens, like most NHL teams that are successful (or are moving in that direction) transition at a lightning pace - they reverse and head in the other direction seamlessly, like an agile, responsive motor boat changing direction.
The Caps typically transition like a large, belching, bilging ocean liner trying to change direction. Small wonder they get bottled, can't generate speed thru neutral, and can't make effective entries - because the opponent that was temporarily dispossessed has made the transition to D faster than the keeps can transition to a connected, up-tempo (or any kind of tempo) O. We're still on our heels on O, while the opponent is on their toes. And when we have to transition to D, all the things we can't do - exit the zone cleanly, up the pace thru neutral, and enter the attack zone with the opponent backing off - are being done by the opponent, because our transition to D seems to start with some or all the Caps having a moment to say "not again" rather than getting on their horse to get the puck back or at least slow the counter-attack.
It was excruciating to watch one team playing NHL hockey in 2023, while the other team seemed stuck in like the early 90s.